4C-9910 Portable Hydraulic Tester (Flow 125 GPM) {0599, 0784, 5050, 5057, 5095} Caterpillar

4C-9910 Portable Hydraulic Tester (Flow 125 GPM) {0599, 0784, 5050, 5057, 5095}


769C 01X

Caterpillar Products: All


Important Safety Information

Illustration 1g02139237

Think Safety

European Union Compliant, ICE marked

Most accidents that involve product operation, maintenance, and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs. A person must be alert to potential hazards. This person should also have the necessary training, skills, and tools to perform these functions properly.

Improper operation, lubrication, maintenance, or repair of this product can be dangerous and could result in injury or death.

Do not operate or perform any lubrication, maintenance, or repair on this product until you have read and understood the Tool Operating Manual.

Safety precautions and warnings are provided in this manual and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons.

The hazards are identified by the "Safety Alert Symbol" and followed by a "Signal Word" such as "DANGER", "WARNING", or "CAUTION". The Safety Alert "WARNING" label is shown below.

A non-exhaustive list of operations that may cause product damage are identified by "NOTICE" labels on the product and in this publication.

Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard. The warnings in this publication and on the product are, therefore, not all inclusive. If a tool, procedure, work method, or operating technique that is not recommended by Caterpillar is used, the operator must be sure that the procedures are safe. The operator must also be sure that the product will not be damaged or made unsafe by any unspecified procedures.

The information, specifications, and illustrations in this publication are based on information that was available at the time that the publication was written. The specifications, torques, pressures, measurements, adjustments, illustrations, and other items can change at any time. These changes can affect the service that is given to the product. Obtain the complete and most current information before you start any job.

When replacement parts are required for this product Caterpillar recommends using Caterpillar replacement parts or parts with equivalent specifications including, but not limited to, physical dimensions, type, strength, and material.

Literature Information

This manual contains safety information, operation instructions and maintenance information and should be stored with the tool group

Some photographs or illustrations in this publication may show details that can be different from your service tool. Guards and covers might have been removed for illustrative purposes.

Continuing improvement and advancement of product design might have caused changes to your service tool, which are not included in this publication.

Whenever a question arises regarding your service tool or this publication, consult Dealer Service Tools (DUST) for the latest available information.

Safety Section

The Safety section lists basic safety precautions.

Read and understand the basic precautions listed in the Safety section before operating or performing maintenance and repair on this service tool.

General Information Section

The General Information section describes tooling functions and features. The section provides useful information on individual parts, additional tooling, and resources.

Operation Section

The Operation section is a reference for the new operator and a refresher for the experienced operator.

Photographs and illustrations guide the operator through correct procedures for using the tool group.

Operating techniques outlined in this publication are basic. Skill and techniques develop as the operator gains knowledge of the service tool and the tools capabilities.

Maintenance Section

The Maintenance section is a guide to tool inspection, cleaning, storage, and tool disposal

Service Parts Section

The Service Parts section is a reference for parts identification and available part numbers.

Safety Icon Nomenclature

Personal Protection/Important Information

Illustration 2g02166423

Personal Protection/Important Information

Prohibited Action

No smoking

Hazard Avoidance

Crushing hazard (foot)

Crushing hazard (hand)

Pinch point

Fire hazard

Electrical Shock - Hazard

Fire hazard


------ WARNING! ------

At operating temperature, the hydraulic tank is hot and under pressure.

Hot oil and components can cause personal injury. Do not allow hot oil or components to contact skin.

Remove the filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand. Remove the filler cap slowly in order to relieve pressure.


------ WARNING! ------

Personal injury or death can result from escaping fluid under pressure.

Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.

Always use a board or cardboard when checking for a leak.



Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "Caterpillar Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Caterpillar products.

Dispose of all fluids according to local regulations and mandates.


To prevent dirt and contaminants from entering the hydraulic system, always plug or cap the lines, fittings, or hoses as they are disconnected.

This action also lessens the chance of oil spills.

General Information

Illustration 3g02786938


The Digital Readout 4C-9910 Portable Hydraulic Tester has been designed for easy connection to hydraulic circuits so that flow, pressure, and temperature can be checked. To facilitate easy operation, all common engineering units can be selected and the display update time can be varied. The tester can take full back pressure up to 500 bar (7250.0 psi) and the built-in loading valve enables many operating conditions to be simulated. The tester can be connected anywhere in the system to test pumps, motors, valves, and cylinders in both flow directions.

Bidirectional Flow Testing

  1. The loading valve gives smooth control of pressure in both flow directions and is protected in both flow directions by two replaceable safety discs which are designed to rupture internally at approximately 7 bar (100.0 psi) over the maximum working pressure. When discs rupture, the oil by-passes the loading valve at low pressure and continues to flow freely through the hydraulic system.

  1. The flow tester can be used in both flow directions but there is a preferred flow direction. Direction indicated by "IN" and "OUT" on the tester block. When the tester is used for reverse flow tests slightly lower accuracies may be obtained, these slight differences are not significant.

  1. The tester is connected to the machine by flexible hoses 1 to 2 m (3 to 6 ft) long. The use of quick disconnect couplings can save time. Make sure that couplings are connected properly. Incorrectly connected couplings can prevent oil flow and cause damage. Elbows, rotary couplings, at the inlet and outlet ports of the tester should be avoided to ensure accurate readings.

  1. After installing the tester, check that all connections are tightened and that oil can flow freely through the system before running machine at full speed. Check that the circuit is correctly connected and that the tester load valve and any shut off valves are opened. Check that quick disconnect couplers are correctly connected.

    Note: Start the pump momentarily to ensure that there is no obstruction which could cause blockage of flow resulting pressure overload.

  1. Caterpillar provides additional external flow meters which can be used with the tester to provide a wider flow range (from 7 to 758 L (2.0 to 200.0 US gpm), consult Caterpillar Service technology Group for details) and to check flows from two locations. The tester can be programmed to accept any external flow meters, see Section ""Programming" " for programming instructions.

  1. An automatic power off system shuts off battery power to the tester after approximately 1 hour. To reactivate the tester, press the "ON" key. User programmed values are not canceled by the auto-off function. Values are canceled if rotary switch is turned to "RESET".


  1. 6V-3136 Caterpillar Photo Pick Up can be used to obtain RPM of rotating shafts. See Table 1.

Analog Output

  1. An analog voltage output is provided and is powered from the testers 9 V battery. This output provides a 0 to 1.5 V DC output for a flow range of 0 to 474 L/min (0 to 125.0 US gpm) passing through the testers integral flow meter. This output can be used as an input signal to chart recorders or suitable data loggers to provide a permanent record of flow variations.

Additional Contact Information

For additional product support questions concerning this tool, contact the Caterpillar Dealer Service Tools Hotline at:

USA: 1-800-542-8665, Option 1International: 1-309-578-7372


Table 1
Bi Directional Hydraulic Tester    
Model No.     4C-9910    
Flow Range        
American Gallons/Minute     3.5 - 125 gpm    
Metric Liters/Minute     13 - 475 L/min    
UK Gallons/Minute     2.9 - 104 gpm    
(psi/bars gauge)    
0 to 500 bar (0 to 7000.0 psi)    
6V-3136 Photo Pick Up
64-2198 Extension Cable
5 m (18.0 ft)    
0 - 6000 rpm    
Ports     #24 SAE O-ring
1 7/8 inch - 12 UN Female    
11.4 kg (25.0 lb.)    
Overall Dimensions    
255 x 215 x 205 mm (10.0 x 8.5 x 8.0 inch)    
Flow Accuracy     1% of indicated flow when used within above flow
range with mineral oil of viscosity 28 centistokes and
pressure of
20 bar (300.0 psi)    
Speed     Within 1% of maximum speed    
Pressure     Within 1.6% of full scale    
Temperature     ±1 degree C    
Batteries Tester :     9 V standard battery
size 5/8 x 1 x 1 x 1 11/16 inch
No. A1604 (USA), 64F22 (Europe), 6AM6 (Japan), PP3 (UK)    
Phototachometer:     1 1/2 V standard battery
1 1/4 inch dia x 2 1/4 inch long
"D" Cell (USA)    

Trouble Shooting With The Hydraulic Tester

This tester is a versatile tool and can be used on hydraulically powered equipment working at pressures up to 48263 kPa (7000.0 psi) and flows from 13 to 473 L/min (3.5 to 125.0 US gpm). The following notes cover general usage and are applicable to many types of machine. For specific tests on Caterpillar machines call Caterpillar Service Technology Group.

Preliminary: Check that tester is installed correctly. Check oil level in tank, pump drive, and valve linkages for damaged parts, external oil leaks.

Table 2
Excessive pump noise, fluctuating pressure

Low flow under no load    
Pump Cavitation caused by:
a) Clogged suction filter
b) Restricted suction line
c) Air leak in pump suction
line, fittings, shaft seals and so on
d) Pump speed too high    
Sections ""Test 1 - Pump In Line Test" ", ""Test B - Tee Test" "    
Decreasing performance as pressure increases on all circuits

On one circuit    
Internal leakage in:
a) Pump
b) Main relief valve

c) Directional control valve

a) Cylinder or hydraulic motor    

Sections ""Test 1 - Pump In Line Test" ", ""Test B - Tee Test" "
Sections ""Overall System and Relief Valve Test" ", ""Control Valve Cylinder Tee Test" "
Sections ""Overall System and Relief Valve Test" ", ""Control Valve Cylinder Tee Test" ", ""Additional Tests to Locate Fault in Control Valve or Cylinder" ", ""Directional Control Valve Inline Test" "
Sections ""Cylinder Test" ", ""Motor Test" "    
Fails to hold load     Internal leakage in:
a) Directional control valve

b) Cross line relief valve
c) Cylinder    

Sections ""Overall System and Relief Valve Test" ", ""Control Valve Cylinder Tee Test" ", ""Additional Tests to Locate Fault in Control Valve or Cylinder" ", ""Directional Control Valve Inline Test" "
Sections ""Directional Control Valve Inline Test" ", ""Cylinder Test" "    

Internal leakage in directional control valves can be caused by wear in mechanical leakages causing spool not to shift fully.



The thermistor temperature transducer is in contact with the oil flow and is displayed on the left-hand side of the digital display. Temperature from the internal transducer is displayed in the "INT" and "TACH" position. Temperature from a remote turbine is displayed in the "EXT" position. Pressing the "F/C" button switches the display from Fahrenheit to Centigrade and the unit selected is indicated by a cursor arrow "V".


A) Flow Meter

The Flow Meter comprises an axial turbine mounted in an aluminum block. The oil flow rotates the turbine and the speed is proportional to the oil velocity. The revolutions of the turbine are measured with a magnetic sensing head. The sensing head feeds a pulse every time a turbine blade goes by, to an electric circuit. The circuit amplifies the pulse, shapes pulse into square wave forms, and has a digital output which is directly proportional to the number of pulses per second. Flow rate is displayed in the right-hand side of the digital display when "INT" or "EXT" are selected. Pressing the units button switches the display to USGPM, IGPM, or LPM and the selection is indicated by a cursor arrow. When the flow rate falls below the minimum allowable, "L" is indicated on the display. When flow rate exceeds the maximum, "H" is indicated on the display.


RPM is displayed in the right-hand side of the digital display when "TACH" is selected on the rotary switch. Pressing the units button switches to "RPM" or "RPM/N" indication. RPM assumes that the sensor provides 1 pulse per revolution of the shaft. "RPM/N" assumes that the sensor provides N pulses each revolution of the shaft.

The value of N can be varied. (See Section on ""Programming" ").

Pressure Gauge

The pressure gauge has a spiral Bourdon tube and the gauge case is filled with glycerine to ensure good dampening on pulsating pressures. The gauge is connected to the turbine block by a fine bore capillary tube. Testers with BUILT-IN load valves have a shuttle valve which automatically reads the highest pressure in both directions of flow. A gauge port is provided in the block for the addition of a low-pressure gauge.

Fast Button

The fast button changes the update time of the display. In some situations quick response to flow rate changes is required. With the cursor arrow highlighting the fast position, the update time is 1/3 second. Otherwise the update time is approximately 1 second. When using fast update, the display will be less stable on flow and shaft speed.


When the selector switch is in the reset position the unit is switched off. All user programmed values (see Section on ""Programming" ") are canceled and the tester reverts to factory set values. Power consumption in this condition is zero.

Illustration 4g02786942

Table 3
Caterpillar Service Tool Compatibility Information    
Suitable for use with Caterpillar Flow Meters and Photo Pick Ups as listed below:    
Caterpillar No.     Description     Ref. no.    
57 L/min (15.0 US gpm) Turbine Flow Meter    
114 L/min (30.0 US gpm) Turbine Flow Meter    
227 L/min (60.0 US gpm) Turbine Flow Meter    
379 L/min (100.0 US gpm) Turbine Flow Meter    
492 L/min (130.0 US gpm) Turbine Flow Meter    
568 L/min (150.0 US gpm) Turbine Flow Meter    
795 L/min (210.0 US gpm) Turbine Flow Meter    


Flow can be passed through the unit in either direction. Before starting machine, ensure that load valve is open by rotating fully counterclockwise. Whichever flow direction is used, the pressure gauge shows highest pressure applied by load valve.

To read flow from built-in flow meter:

  1. Turn rotary switch to reset. Count 5 seconds. Turn rotary switch to "INT". Display will show temperature at right-hand end of digital display and flow at left-hand end. Flow rate is displayed at right-hand end of display. If flow is too low to register, "L" is displayed. Use "UNITS" button to select US gpm, Imperial gpm, or liter/min display. "FAST" button selects fast or slow reading interval which can be useful when transient flows make readings appear unstable.

To read flow from external flow meter:

  1. Plug one end of cable, Caterpillar # 4C-9438 Cable into the five pin socket on the external flow meter. Plug the other end into the five pin socket marked "EXT.FLOW" on the 4C-9910 Portable Hydraulic Tester .

  1. Switch rotary selector switch on the tester to "EXT" position. If no characters appear on display, proceed to Step 3 below. If any characters appear on digital display depress "ON" button once, display will then become blank.

  1. Having obtained a blank display, hold down the "°F/°C" button while depressing once the "ON" button. Display will activate. Release all buttons.

  1. Look at the three left-hand digits. Depress "FAST" button repeatedly until the three left-hand digits read the same as the LT number referenced on the preceding page.

  1. Depress "ON" button once to obtain blank display.

  1. Depress "ON" button once to activate display. Display will show the LT number referenced.

  1. Depress once the button marked either "°F/°C", "FAST", or "UNITS". Display will now show flow and temperature of oil passing through the external flow meter.

If additional information concerning programming of external flow meter is required, refer to the instructions supplied with the external flow meter.

To read RPM

  1. Insert 2 "D" cells into battery holder at back of the Portable Tester, negative pole enters the holder first.

  1. Plug one end of cable, Caterpillar # 64-2198 Cable , into Caterpillar 6V-6136 Photo Pick Up . Plug other end into "TACH" Socket on the 4C-9910 Portable Hydraulic Tester

  1. Switch rotary selector switch to "TACH" position.

  1. Apply one piece of light reflective tape to shaft.

  1. Depress "UNITS" button until cursor or V symbol on the digital display is positioned above RPM decal.

  1. Point photo light at reflective tape from a distance of 152 to 305 mm (6.0 to 12.0 inch), shaft rpm will be displayed.

To read RPM of slowly rotating shafts, apply more than one piece of reflective tape to obtain a higher frequency signal. In this case follow instructions in Steps 1 to 3 above. Then proceed as below:

  1. Apply required number of pieces of reflective tape to shaft, for example assume three pieces.

  1. Depress "UNITS" button until V symbol on digital display is positioned above RPM/N decal.

  1. Depress "ON" button once to obtain blank display.

  1. Having obtained blank display hold down the "°F/°C" button while depressing once the "On" button. Display will activate.

  1. Since there are three pieces of tape, program the display to read 03.000. Use "UNITS" button to position the symbol under the digit to be changed, then repeatedly depress the "FAST" button to change digit to desired value.

  1. Depress "On" button once to obtain a blank display. Press "On" button once again to activate display.

  1. Point photo light at reflective tape from a distance of 152 to 305 mm (6.0 to 12.0 inch). Actual shaft rpm will be displayed. The tester divides the frequency of light pulses by the programmed value of three.

Instructions For Using the 4C-9910 Portable Hydraulic Tester

The tester is designed to measure pressure, flow, temperature, and rpm. Tester can measure full system pressure up to 483 bar (7000.0 psi) and measure flow in both directions for motor and cylinder testing.

  1. Make all tests at operating temperatures because as the oil temperature increases oil becomes thinner and any internal leakage becomes greater.

  1. Testing will be easier and faster if quick disconnect couplers are used to attach the Test Unit.

  1. There are two basic test setups.

    1. The In Line test to check out pumps, entire systems, and also monitoring operating conditions.

    1. The Tee Test to check out pumps, directional control valves, and the overall system condition.

  1. Make preliminary check of the hydraulic systems, oil supply, pump rotation, filters, oil lines, and cylinder rods. Look for external leaks should be made prior to installing the Hydraulic Tester.

Installing The Test Unit

  1. Connect the Tester to the circuit, see Section ""Specifications" " for Port Sizes. The inlet and outlet ports are marked on the turbine block. Use hoses and fittings of sufficient diameter for the flow being tested. Avoid restrictions at inlet and outlet ports of the Tester. Also avoid sharp bends because high-pressure hoses will deflect and straighten under pressure.

  1. When the pressure loading valve is used, ensure that valve is fully opened by turning the knob counterclockwise.

  1. When no flow is passing through the turbine, the display will read "L" for "LOW" flow.

  1. When low-pressure testing is required, connect the optional low-pressure gauge with quick disconnect coupler. Connect only after the pressure has been checked on the high-pressure gauge. REMEMBER to disconnect the low-pressure gauge for high pressure tests otherwise the gauge will be damaged.

    Note: An automatic cutout valve which protects the LP gauge is available. Consult sales office.

Standard Test Conditions

  1. Position the Hydraulic Test Unit as described in Sections ""Test 1 - Pump In Line Test" " and ""Test B - Tee Test" ".

  1. Open loading valve. (Rotate counterclockwise) and select high flow range.

  1. Start pump momentarily to ensure that oil flows freely through the hydraulic system, then run pump at normal maximum speed. Do not change pump speed while using the loading valve.

  1. Slowly close Test Unit Loading Valve to develop desired pressure. Run the machine until normal operating temperature is reached.

  1. Open the Tester Loading Valve and proceed with required test procedure (see Sections ""Test 1 - Pump In Line Test" " and ""Test B - Tee Test" ".

  1. Keep a record of flow reading at various operating pressures for comparison of test results. The machine Manufacturers service manual should be consulted.

Test 1 - Pump In Line Test

Illustration 5g02786946

  1. Install the Tester into the system between the pump outlet port and the inlet to the directional control valve.

  1. Open Tester Loading Valve to read maximum pump flow at minimum pressure.

  1. Close Loading Valve slowly to increase pressure and note reduction of flow as the pressure is increased to maximum pump pressure to determine pump condition.

  1. Pump flow at rated pressure can now be checked against the pump manufacturers specifications. The decrease in flow from minimum pressure to maximum pressure determines the pump condition. Typically a worn or damaged pump will lose 20-30%. A pump that delivers low flow at both minimum and maximum pressure indicates suction problems. Blocked suction filters and pump cavitation problems can also be checked by recording the pump flow at various engine speeds.

  1. The Tester can be used at several points in the circuit. The machine can be used under normal working conditions to evaluate the performance of circuit elements, such as pump, control valve, cylinder, and hydraulic motor.

Test B - Tee Test

Illustration 6g02786951

  1. A Tee must be installed at one point between the pump and control valve then connected to the "IN" port of the Tester. The "OUT" port of the tester is connected back to the tank. Make sure that loading valve is open.

    1. Pump Test. Disconnect and plug connection to control valve and proceed as in Step 2, 3 and 4, of Section ""Test 1 - Pump In Line Test" ".

Overall System and Relief Valve Test

(For Relief valve integral with Directional Control Valve)

  1. Connect control valve to Tee. Operate control valve to extend the cylinder to end of stroke.

  1. Close the Tester Loading Valve while watching pressure and flow meter reading. Pressure will increase until relief valve opens at which point flow reading will return to "Zero". Note or record pressure. Adjust the relief valve if the pressure is below the recommended setting. It is not unusual for a relief valve to start cracking open below the maximum pressure setting causing considerable leakage and loss of machine performance. The cracking pressure can be checked by increasing the pressure slowly and noting the pressure at which the flow starts falling rapidly to zero. The maximum relief valve setting is when the flow is at zero.

Control Valve Cylinder Tee Test

  1. Put control valve in power position. (On multiple spool valves, only one spool should be in a power position at any one time). The cylinder should be extended to the end of the stroke.

  1. Close Test Unit Loading Valve slowly while recording pressure and flow rate.

  1. Repeat Step 2 for power position, for all spools of all control valves.

  1. If all components are in good operating condition, pressure and flow measurements should be the same as in pump test Section ""Test 1 - Pump In Line Test" ".

  1. If a decrease in flow of any control valve position is noted, leakage is indicated in this control valve or cylinder. See Section ""Additional Tests to Locate Fault in Control Valve or Cylinder" " for test routine to determine which is at fault.

  1. The relief valve is at fault if the decrease in flow is the same for the control valves in all positions.

    Note: Decrease in flow can also indicate some other leak is present in the control valve such as a defective casting. Always check the relief valve FIRST.

Additional Tests to Locate Fault in Control Valve or Cylinder

(See Step 5 in Section ""Control Valve Cylinder Tee Test" "). Disconnect line to cylinder and plug valve port.

  1. Place control valve handle in position where greatest decrease of flow was noted.

  1. Close Test Unit Loading Valve and record both pressure and flow.

  1. If the SAME decrease in flow is noted, as in test per Step 5 in Section ""Control Valve Cylinder Tee Test" ", then the control valve is at fault. HOWEVER, if the flow readings are now higher and comparable to the other control valves, then a faulty cylinder is indicated.

Directional Control Valve In line Test

Illustration 7g02786953

  1. To check relief valve pressure setting where relief valves are integral with control valve, install flow meter in the cylinder line as shown in Figure 7, ensuring that loading valve is open (turn counterclockwise). Start pump and operate the lever on the valve in which the tester is situated to raise load. Slowly close the uploading valve (turn clockwise), reading pressure and flow. Continue until loading valve is fully closed, pressure reading obtained is then relief valve pressure. Compare with manufacturers recommendations. Adjust relief valve if necessary. Using bidirectional flow testers, the cylinder and valve may be tested in the opposite direction by operating the lever to retract the cylinder.

  1. Control Valve Leakage

    With flow meter installed as in Step 1, repeat tests and compare flow readings obtained for comparable pump test Step 3 of Section ""Test 1 - Pump In Line Test" ". Differences in flow readings indicate leakage within control valve. Repeat test for all power ports to determine valve condition. Replace control valve block or valve segment where necessary.

Cylinder Test

See Figure 7.

  1. If the cylinder is slow in operation, or cylinder creeps under load, the following test should be carried out to check the cylinder seals.

    Install the flow meter in line as shown in Figure 7. Actuate cylinder to raise and lower the load. Note flow and pressure readings, also note the time taken by the cylinder to reach full stroke. Compare all readings with manufacturers recommended figures. If flow is correct but time to extend cylinder is greater than expected, leakage across the cylinder seals is indicated. If flow is lower than expected, investigate control valve function. See Section ""Directional Control Valve Inline Test" ".

Motor Test

  1. Motor performance is checked by measuring the flow and comparing to the equivalent motor speed. Install the tester or remote flow block in the line upstream of the motor as indicated by the arrow in Figure 7. Fully open the loading valve and operate the directional control valve ensuring the motor rotates in the correct direction. Allow motor to run under normal load. Note flow and pressure readings. If flow is below manufacturers data sheet, or lower than pump test in Section ""Test 1 - Pump In Line Test" ", investigate control valve function. See Section ""Directional Control Valve Inline Test" ".

    Note: The motor may only be tested in reverse if the motor has an external drain. Do not pressurize the outlet port of the motor without first checking the allowable back pressure with the manufacturer.

Motor Leakage

  1. Measure hydraulic motor rpm with tachometer when motor is working at normal pressure. If the motor speed is low, and the inlet flow in Section ""Motor Test" " Step 1 is found to be correct, internal leakage in the motor is indicated. Check the motor leakage by installing the remote flow block in the motor case drain.

    Note: Most motors not fitted with high-pressure shaft seals have a maximum case drain pressure of 1 bar (14.5 psi).

  1. When the motor does not have an external drain, or the motor cannot be back pressure loaded, connect tester in the other line. Repeat the test in Section ""Motor Test" " Step 1 and Step 1 in this section.

Alternative Cylinder and Motor Test

Illustration 8g02786956

  1. Both motors and cylinders may also be tested as shown in Figure 8. Disconnect the two lines from the motor and connect the tester into these lines. Fully open the loading valve, start the pump, and bias the directional valve to allow flow to the inlet port of the tester. Slowly close the loading valve by turning clockwise and note the flow and pressure. If the flow is below the manufacturers data, or lower than the pump test in Section ""Test 1 - Pump In Line Test" ", investigate the control valve function. See Section ""Directional Control Valve Inline Test" ". If the flow is correct, and the speed is slow, a defective motor or cylinder is indicated.

    Operate the directional valve to reverse the flow through the tester and record the flow throughout the pressure gauge.

Photo Tachometer

General Description

The Photo Tachometer consists of the Photo Tach Head, Reflective tape and connecting cable.

RPM is displayed in the right-hand side of the digital display when "TACH" is selected on the rotary switch. Pressing the units button switches to "RPM" or "RPM/N". "RPM" assumes that the sensor provides 1 pulse per revolution of the shaft. "RPM/N" assumes that the sensor provides N pulses each revolution of the shaft. The value of N can be varied (See Section on ""Programming" ") the tester.

Photo Tach Head

The Photo Tach Head senses the speed of a rotating body without physical contact. The design permits Photo Tach Head to be used over a wide range of distances from the rotating body.

Object Preparation

The Photo Tach Head will only sense the change in reflected light from a moving object. Therefore, a rotating shaft with a uniform reflective surface must be marked with pieces if reflective tape supplied with the photo tachometer. Select a convenient position on the shaft, pulley, or coupling which has a minimum diameter of 35 mm (1.4 inch). Larger diameter shafts will give better results particularly at high speeds. The surface should be free from bolt holes and keyways. Clean the surface and fix a piece of reflective tape, approximately 20 mm (0.8 inch) long. Paint or cover the remainder of the shaft with matte black or use large pieces of reflective tape if not sufficient contrast.

For shaft speeds lower than 800 rpm use 2 pieces of reflective tape, and program the "TACH" channel with a factor of 2.

Obtaining a Reading

Connect the cable in the Tach Head and attach the magnetic base. Fix the magnetic base in a suitable position and aim the light at the rotating object. Switch on the tester, select "TACH" and position the Photo Tach Head 150 mm (6.0 inch) away from the object and read the rpm directly on the meter. If no reading is obtained move the head closer to the shaft. If the reading is fluctuating, select slow update and increase the distance from the shaft until a steady reading is obtained. The distance of the Photo Tach Head from the object will vary. Distance depends on the ambient lighting, size of object, amount of contrast and the speed of the object. Certain types of ambient lighting may require shading of the rotating object or applying a larger reflective mark will correct the situation.

Battery Replacement

The Tester Meter battery should be replaced if the display is faint. The lamp batteries in the tester case should be replaced when the lamp intensity becomes too dim to be effective. The Tester battery is a 9 V PP3. The tacho lamp uses two HP2 (D cell) R20 HP batteries. On DHT testers remove the battery cap located on rear of the case and remove packing piece, fit two batteries.

Service Instructions

If the flow meter does not indicate flow:


  1. Turn the selector switch to "INT". If the digital display is absent press the "ON" button. If the display is faint or still absent check the condition of the battery and battery connections located in the front panel. Replace batteries if necessary.

  1. If the flow meter displays a valid temperature, but does not show flow when in the "INT" position, the turbine possibly has become jammed by debris. Possibly pieces of O-ring or PFTE tape. Remove and clean the turbine as in Section ""TURBINE" ".


Illustration 9g02786976

  1. Before removing the turbine assembly for cleaning note the angular position of the turbine assembly in the main body. When reassembling, the assembly must be replaced with the flow straighteners in the same position. To remove turbine assembly, unscrew retainer from inside the inlet port. Grip one flute of the turbine flow straightener with soft nose pliers and gently pull out of the main body. Do not rotate the assembly. Remove debris and wash in clean organic solvent. Turbine should revolve freely when blown along the flow straightener.

  1. Ensure that the turbine block is also free of debris. Replace the turbine assembly in the same angular position noted prior to removal.

  1. The turbine can be driven with air flow to check the flow meter. For this test the loading valve must be open. Direct the air flow through the inlet port, switch tester to "INT". The air should rotate the turbine and the digital display indicate flow. Do not overspeed the turbine. If no flow reading can be obtained refer to Section ""Complete Overhaul" ". The Overhaul techniques should only be carried out by technicians trained in the maintenance of flow meters.

Loading Valve

Illustration 10g02786980

If the loading valve becomes difficult to turn under pressure or will not close, remove the four socket screws. Check for worn valve seat, damaged, or leaking seals and contamination.

Note: If the pressure does not increase progressively when the loading valve is operated, check if the safety discs have been ruptured. Assemble the loading valve into the flow block ensuring that the guide pin is located in the slot on the poppet valve.

Safety Discs

Illustration 11g02786996

The loading valve is fitted with two safety discs which are designed to rupture internally at approximately 7 bar (101.5 psi) over the maximum pressure. When these discs fail, the loading valve becomes inoperative and the oil flows freely downstream.

To replace the safety discs, remove the loading valve assembly from the flow block. Unscrew the safety disc holder from the valve by carefully gripping the valve on the 30 mm (1.2 inch) diameter. Remove the disc spacer and the ruptured discs from the valve and the disc holder. Carefully perform the two discs by pressing by hand between the disc holder and spacer. Place one new disc inside the valve and replace the spacer. Place a second disc on top of the spacer and screw in the disc holder. Tighten the holder to 54.2 N·m (40 lb ft).

Complete Overhaul Instructions


This manual is not intended to provide information regarding the repair of the electronic circuit board. Such faults are difficult to trace without specialized equipment and training. Where electronic faults are suspected the tester should be returned to the Sales Office. Physical damage to display and keyboard may occur and can be checked as follows.

To remove Top Panel

Remove 6 screws from top panel and angle up the bottom of the panel 51 to 76 mm (2.0 to 3.0 inch). Move panel forward 25 mm (1.0 inch) then lift 51 to 76 mm (2.0 to 3.0 inch). Using 11/16 inch and 9/16 inch AF spanners, disconnect the copper pipe at the pressure gauge. Disconnect the transducer socket from the circuit board by carefully easing out the plug with a small screwdriver. Remove the two tach battery leads and lift out panel.

Pressure Gauge

The glycerine filled gauge is connected to the block by a capillary tube. If this not working, clean tube with organic solvent and blow air through line.

If the gauge is damaged, a replacement should be made. Ensure that the copper sealing ring is in good condition and the connection is securely tightened.


Illustration 12g02786998

Panel Plug on Circuit Board

Temperature Signal Pins 1 and 2

Earth Pin 5

Flow Transducer Signal Pins 3 and 4

To check the temperature reading on the display, connect a 10,000 ohm 1 percent resistor between pins 1 and 2. Switch selector switch to "TACH" or "INT" and check that the display reads 50.5 degrees C / 2 degrees C. Consult sales office for further information.


Illustration 13g02787001


Temperature Signal Pins 1 and 2

Coil Pins 3 and 4

Screen Pin 5

Connect voltmeter (20,000 ohm/volt) between pins 1 and 2. Check that resistance is 38,000 ohms at 20° C (68.0 ° F) and 30,000 ohms at 30° C (86.0° F). Check that coil resistance is 4000 ohms between pins 3 and 4. If low resistance is obtained, check socket wiring.


If the turbine does not run free after being cleaned in solvent, the turbine bearing should be replaced. Carefully unscrew the turbine straighteners, remove the turbine rotor, and disassemble the turbine circlips. Replace the bearing and circlips, reassemble straighteners with Loctite type thread sealant.

Transducer Adjustment

Illustration 14g02787007

Illustration 15g02787008

Replace turbine, blow air into inlet port. Connect transducer plug to Voltmeter. Switch to A/C. Meter should read 1 to 2 V at maximum flow indication. If reading below 1/4 volt at minimum flow indication, adjust position of transducer. Loosen sleeve nut and carefully screw in transducer until the turbine slows to a stop and the voltage falls to zero. Reverse turn by 1/8 of a turn and retighten sleeve nut. Repeat voltmeter test and if not within voltage range replace transducer.

Replacing Components


Remove the four M3 nuts holding the circuit boards to the panel. Lift away circuit boards in order to gain access to the display. Lift out the display and replace with new display. The cutout in the dark edge of the display should face to the right-hand side when the circuit board is positioned for normal viewing.


The EPROM is located on the top circuit board and is immediately visible once the front panel is removed. EPROM has a serial no. label. The EPROM has a notch at one end. Ensure the notch on the new EPROM faces the same way as the old one and that the pins are correctly located in the socket.


Remove circuit boards as detailed above. Unscrew the four M3 nuts holding the keypad retaining plate in position. Lift away the plate and replace keypad. A replacement complete top panel precalibrated to any tester can be supplied if the serial number located on the block is given.

Circuit Board

The replacement of a display or keypad will not affect the correct operation of the flow measuring circuitry. Correct operation of the flow circuitry can be checked by connecting an accurate audio frequency generator between pins 3 and 4.

Note: The frequency generator signal must be fully floating, not referenced to earth.

When set to LPM, the relation between frequency and flow will be as follows:

Table 4
Displayed Flow (in LPM)     =     Frequency input (Hz) x 60    
        Programmed calibration factor    

An unstable or incorrect reading indicates a fault with the flow circuitry. Return the unit to sales office.

Photo Tachometer

Checking the operation the photo tachometer circuit is similar to checking the flow circuit. Connect an accurate audio frequency generator between pins 1 (signal) and pin 2 (ground) of the "TACH" socket on the front of the panel. The frequency generator signal in this case must be referenced to earth.

When set to "RPM" the relation between frequency and RPM will be:

Displayed RPM = Frequency input (Hz) x 60.

An unstable reading indicates a fault with the TACH circuitry.


After reassembling the components, ensure that the top panel is resecured using 152 mm (6.0 inch) by 13 mm (0.5 inch) long self tapping screws. In all cases of communication with Sales the Office for replacement parts, the Model Number and Serial Number on tester block is essential. Records are maintained relating the frequency figures of each flowmeter against Serial Number.

Caterpillar Information System:

C7 and C9 On-highway Engines Maintenance Interval Schedule - C7 Engines with Shallow Sumps that are Used in School Bus Applications
C7 and C9 On-highway Engines Maintenance Interval Schedule - C7 Engines with Deep Sumps that are Used in School Bus Applications
9U-5000 Series Hydraulic Test Bench {0599, 0738} 9U-5000 Series Hydraulic Test Bench {0599, 0738}
C13 Engine for Combat and Tactical Vehicles Exhaust Manifold
2011/12/01 An Improved 5P-8500 Key Is Now Available {1416, 1416, 7000, 7000}
Diesel Particulate Filter Regeneration on C7.1 Engines{108F} Diesel Particulate Filter Regeneration on C7.1 Engines{108F}
New Engine Software Is Available for Tier 4 Interim C9.3 Through C18 Industrial and Machine Engines{1901, 1902, 1920} New Engine Software Is Available for Tier 4 Interim C9.3 Through C18 Industrial and Machine Engines{1901, 1902, 1920}
Revised Start-Up Procedure For Uninterruptible Power Supply UPSB 125/130 {4480} Revised Start-Up Procedure For Uninterruptible Power Supply UPSB 125/130 {4480}
2012/01/12 A New Hose Is Used in the Fuel Filter Lines on C175-16 Generator Set Engines {1261, 1274}
2011/12/19 New Fuel Injectors and New Software Are Used for C175-16 Generator Set Engines {1251, 1254, 1290, 1713, 1901, 1920}
C7 and C9 On-highway Engines Fluid Recommendations
C7 and C9 On-highway Engines Refill Capacities
C7 and C9 On-highway Engines Air Compressor - Check
C7 and C9 On-highway Engines Compression Brake - Inspect/Adjust/Replace - Cat Compression Brake
CX48-P2300 Petroleum Transmission Transmission Relief Valve (Transmission Hydraulic Control)
CX48-P2300 Petroleum Transmission Transmission Flexible Coupling
CX48-P2300 Petroleum Transmission Transmission Flexible Coupling
CX48-P2300 Petroleum Transmission Transmission Flexible Coupling
2012/01/06 New Location for the Air Inlet Temperature Sensor on C175-16 Generator Set Engines {1439, 7400}
C11 and C13 Engines Camshaft
2011/11/29 Fuel Injection Pump on Certain C6.6 and C6.4 Engines {1251, 1274}
345D MHPU and 349D MHPU Mobile Hydraulic Power Units Machine Security System - If Equipped
3114, 3116, 3126 Engines Connecting Rod
C13 Engine for Combat and Tactical Vehicles Camshaft
Back to top
The names Caterpillar, John Deere, JD, JCB, Hyundai or any other original equipment manufacturers are registered trademarks of the respective original equipment manufacturers. All names, descriptions, numbers and symbols are used for reference purposes only.
CH-Part.com is in no way associated with any of the manufacturers we have listed. All manufacturer's names and descriptions are for reference only.