1994/09/26 Caterpillar

Caterpillar Machines Equipped With A Dust Ejector

Definition

The exhaust ejector is a device used to remove excess dirt from the precleaner. This is accomplished by passing the dirt out via exhaust gases.

Operation

The exhaust ejector removes the excess dirt by applying a suction to a fitting in the side of the precleaner. This suction is developed by exhaust gas rushing through a nozzle or, in later years, through a triple lobed venturi. The dust is removed from the "floor" of the precleaner, sucked through the exhaust tube (hose), then exhausted out the stack.

There are two types of design relationships between the dust ejector tube and the venturi. One type is completely self contained in the muffler or stack such as the 140G (Illustration 2) or the early D10 (Illustration 3). The other type has the dust tube welded into the muffler with the venturi in a separate exhaust stack such as the 970F or D8N (Illustration 4).

The self contained type usually is trouble free, except when damaged either by vibration or external bumps. The center tube is usually not in the correct position after this occurs.

The two piece system will not operate properly when the two pieces, muffler and exhaust stack, are not assembled to the proper engagement length. THIS ENGAGEMENT LENGTH IS CRITICAL! The position of the tube, that extends out of the outlet pipe of the muffler, must extend up into the stack until the outlet of the dust tube is in a special position relative to the narrowest portion of the nozzle or venturi. This is the point which creates the highest vacuum and varies with ejector stack nozzle design.

If the ejector is the 360 degree cone type, the position for the end of the dust tube relative to the narrow throat is about 6.0 mm (.25 in) above the throat (downstream). See Illustration 1. If the ejector is the triple fluted design, then the outlet of the dust tube needs to be positioned 25 to 30 mm (1.0 to 1.2 in) below the narrowest portion of the flutes (upstream). All newer pipes have the triple flute design. Look into the end of the pipe to see which type of nozzle you have. See Illustration 1.

Illustration 1. (A) End view of triple fluted ejector. (B) End view of 360 degree cone ejector.

To check this relationship, convenient tools for determining the position of the nozzle include the 9U-5155 O-Ring Sizer or a large socket with an extension.

Mufflers, which are equipped with a dust ejector tube and need an exhaust stack to supply the venturi, are now manufactured with two small rectangular lugs on the outside of the outlet pipe. These lugs are the STOPS for the exhaust stack. The stack should be driven on until the bottom edge of the stack contacts the lugs. This provides for proper muffler/stack engagement and thus dust tube/venturi relationship (Illustration 4).

The stacks are also manufactured with rectangular lugs on the outer skin. These lugs are to ease assembly and disassembly of the stack to the muffler. This provides a place to hammer and/or pry (Illustration 4). Alignment of the stack lugs and the muffler lugs is NOT required.

Illustration 2. (1) Muffler assembly (includes ejector), (2) Dust flow. Bold arrows indicate exhaust flow.

Illustration 3. (3) Ejector assembly, (4) Dust flow. Bold arrows indicate exhaust flow.

Illustration 4. Two-Piece Example: (5) Ejector stack, (6) Dust flow, (7) Two stack removal/assembly lugs approximately 180° apart (only one lug shown for clarity), (8) muffler, (9) Two engagement lugs on muffler approximately 180° apart (only one lug shown for clarity). Distance (A) as specified in text. Bold arrows indicate exhaust flow.

NOTE: Alignment of (7) stack removal/assembly lugs and (8) engagement lugs NOT required.

Problems

Problems occur with the two-piece ejector system when installing one new part on an old part and the proper engagement length is not maintained, because of dimpling of the old part by the clamp. This places the end of the tube into a high pressure area of the exhaust stack.

Another problem occurs when one part is damaged by rust or external bump and a length of stack is removed. This places the dust tube too high in the stack so suction becomes very low or slightly pressurized.

Also problems develop when a customer removes the exhaust stack and replaces it with a plain pipe. This produces no suction and will slightly pressurize the dust tube.

Other items to look for are exhaust pipe rain caps that are seized or sticking and add on's ahead of the precleaner or extended precleaner stacks. These items or debris on the intake screen add restriction as air flow increases and the suction produced by the exhaust ejector must exceed this or back flow will result. On some machines there is a high likelihood of his happening, so one-way check valves are installed. On the 826C, it is built into the side of the precleaner. On large tractors, it is a separate valve installed in the ejector line. A list of these valves is included for your reference. A valve may be added to any existing ejector line as long as the valve connections are the same size as the ejector hose. Install the valve making sure the installation bracket is towards the top of the valve and the flapper is down, opening towards the muffler (gravity operates the flapper door).

Troubleshooting

The most common complaints, when there is a dust ejector problem, are the sooting of air cleaner elements or the filter elements have a very short life in dusty conditions.

If the system has been functioning fine and then quits, the three most probable causes are:

* The ejector tube breaking loose from the muffler

* The hose and/or tube connecting the muffler to the precleaner has broken or has had a hole worn into it

* An increase in the restriction of the air intake system before the precleaner

To check the dust ejector tube, simply examine where the tube comes out for the muffler. If there is cracking or the tube can be moved by hand, then the loose tube is the problem.

If the tube is secure, then check for vacuum in the tube by removing the ejector hose from the precleaner fitting. Hold a stiff paper card adjacent to the hose hooked to the muffler. If the card is sucked to the end of the hose lightly at low idle and with more force at high idle, the dust ejector tube and hose are functioning. This indicates there are no holes in the hose and the relative position between the ejector tube and nozzle is correct.

This isolates the problem to excessive restriction at the precleaner. Check the inlet screen for plugging and the top of the cyclonic tubes for debris. Also, examine inside the fitting in the side of the precleaner. Check for melted tubes. These tubes are made from plastic and some are usually destroyed when there is a back flow of exhaust. Melted tubes may increase the interior restriction of the precleaner and reduce the effectiveness of the precleaner.

If the dust ejector system has not worked form the first, then the most probable cause is an incorrect engagement length of the exhaust pipe with the muffler. Use the "stiff card suction check" to confirm the lack of suction. Then adjust the exhaust pipe to the correct engagement length. Recheck for suction.