Introduction

NOTE: For Specifications with illustrations, make reference to Specifications For 3208 Industrial Engine, SENR3687. If the Specifications in SENR3687 are not the same as in the Systems Operation and the Testing & Adjusting, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

Fuel System

The Sleeve Metering Fuel System (SMFS) is a pressure type fuel system. The name for the fuel system is from the method used to control the amount of fuel sent to the cylinders. This fuel system has a fuel injection pump for each cylinder of the engine. It also has a fuel transfer pump on the front of the fuel injection pump housing. The governor is on the rear of the fuel injection pump housing.

The drive gear for the fuel transfer pump is on the front of the camshaft for the fuel injection pumps. The carrier for the governor weights is bolted to the rear of the camshaft for the fuel injection pumps. The fuel injection pump housing has a bearing at each end to support the camshaft. The camshaft for the sleeve metering fuel system is driven by the timing gears at the front of the engine.

The fuel injection pumps, lifters and rollers, and the camshaft are all inside of the fuel injection pump housing. The fuel injection pump housing and the governor housing are full of fuel at transfer pump pressure (fuel system pressure).

NOTICE
Diesel fuel is the only lubrication for the moving parts in the fuel transfer pump, fuel injection pump housing and the governor. The fuel injection pump housing must be full of fuel before turning the camshaft.

This fuel system has governor weights, a thrust collar and two governor springs. Rotation of the shaft for governor control, compression of the governor springs, movement of connecting linkage in the governor and fuel injection pump housing controls the amount of fuel sent to the engine cylinders.

In addition to the SMFS, later model engines may be equipped with the Heavy Sleeve Metering Fuel System (HSMFS), or a fuel system that contains features from the earlier (SMFS) and the (HSMFS). The SMFS, HSMFS, and the hybrid fuel systems all function similarly. The hybrid and HSMFS have bolted spill shields, a pressure relief valve returns excess fuel to the tank, square bypass opening port plungers, and overpressure vent to inlet on the fuel inlet flange. Additionally the HSMFS has thicker walled sleeves to reduce high pressure fuel bleed off, side control levers and high rate smoke limiter without preload. The HSMFS is used with Caterpillar DIFN (Direct Injection Fuel Nozzles). The hybrid fuel system uses 7000 series nozzles.

Sleeve Metering Fuel System (SMFS)

Sleeve Metering Fuel System (SMFS) Fuel Flow Schematic
(1) Fuel priming pump (closed position). (2) Fuel priming pump (open position). (3) Return line for constant purge valve. (4) Constant purge valve. (5) Manual purge valve. (6) Fuel injection nozzle. (7) Fuel tank. (8) Check valve. (9) Check valve. (10) Check valve. (11) Fuel inlet line. (12) Water separator. (13) Fuel filter. (14) Fuel line. (15) Fuel transfer pump. (16) Fuel bypass valve. (17) Camshaft. (18) Fuel injection pump housing.

Fuel from fuel tank (7) is pulled by fuel transfer pump (15) through water separator (12) (if so equipped) and fuel filter (13). From fuel filter (13) the fuel goes to fuel injection pump housing (18). The fuel goes to fuel injection pump housing (18) at the top and goes through an inside passage to fuel transfer pump (15).

From fuel transfer pump (15), fuel under pressure, fills the fuel injection pump housing (18). Pressure of the fuel in fuel injection pump housing (18) is controlled by fuel bypass valve (16). Pressure of the fuel at Full Load is 205 ± 35 kPa (30 ± 5 psi). If the pressure of fuel in fuel injection pump housing (18) gets too high, fuel bypass valve (16) will move (open) to let some of the fuel return to the inlet of fuel transfer pump (15).

Flow Of Fuel Using The Priming Pump (SMFS)

When the handle of fuel priming pump (2) is pulled out, negative air pressure in fuel priming pump (2) opens check valve (8) and pulls fuel from fuel tank (7). Pushing the handle in closes check valve (8) and opens check valve (9). This pushes air and/or fuel into fuel injection pump housing (18) through the fuel passages and check valve (10). More operation of fuel priming pump (2) will pull fuel from fuel tank (7) until the fuel lines, fuel filter (13) and fuel injection pump housing (18) are full of fuel. Do this until the flow of fuel from manual purge valve (5) is free of air bubbles. Later model SMFS engines are not equipped with a constant purge valve. On later model engines the excess fuel flow will return to tank (7) through fuel bypass valve (16).

Constant Purge Valve (SMFS Only)

Constant Purge Valve
(4) Constant purge valve. (D) Check valve.

At high idle, the constant purge valve (4) lets approximately 9 gallons of fuel per hour go back to fuel tank (7). This fuel goes back to fuel tank (7) through return line for constant purge valve (3). This flow of fuel removes air from fuel injection pump housing (18) and also helps to cool the fuel injection pump. Check constant purge valve (4) makes a restriction in this flow of fuel until the pressure in fuel injection pump housing (18) is at 48 ± 7 kPa (7 ± 1 psi). Later model engines are not equipped with a constant purge valve. Any excess fuel flow will return to fuel tank (7) through fuel bypass valve (16).

Heavy Sleeve Metering Fuel System (HSMFS)

Heavy Sleeve Metering Fuel System (HSMFS) Fuel Flow Schematic
(1) Fuel priming pump (closed position). (2) Fuel priming pump (open position). (3) Return line for pressure relief. (4) Pressure relief to pump inlet. (5) Fuel injection nozzle. (6) Fuel tank. (7) Check valve. (8) Check valve. (9) Check valve. (10) Fuel bypass valve (with purge orifice). (11) Fuel inlet line. (12) Water separator. (13) Fuel filter. (14) Fuel line (to fuel injection pump). (15) Fuel transfer pump. (16) Camshaft. (17) Fuel injection pump housing.

Fuel from fuel tank (6) is pulled by fuel transfer pump (15) through water separator (12) (if so equipped) and fuel filter (13). From fuel filter (13) the fuel goes to fuel injection pump housing (17). The fuel goes in the fuel injection pump housing (17) at the top and goes through an inside passage to fuel transfer pump (15). Fuel under pressure fills the fuel injection pump housing (17). Fuel injection pump housing pressure is controlled by fuel bypass valve (10).

Pressure of the fuel at Full Load is 255 ± 48 kPa (37 ± 7 psi). If the fuel pressure in the fuel injection pump housing (17) gets too high, fuel bypass valve (10) will move (open) to let some of the fuel return to the fuel tank (6). If return line for pressure relief (3) should become blocked the pressure relief to pump inlet (4) will open at 360 ± 70 kPa (52 ± 10 psi). This pressure relief to pump inlet (4) is intended to provide return to tank capabilities, but lip seals life will be shortened.

Flow Of Fuel Using The Priming Pump (HSMFS)

When the handle of fuel priming pump (2) is pulled out, negative air pressure in fuel priming pump (2) opens check valve (7) and pulls fuel from fuel tank (6). Pushing the handle in closes check valve (7) and opens check valve (8). This pushes air and/or fuel into the fuel injection pump housing (17) through the fuel passages and check valve (9). Air trapped in the fuel injection pump gallery will vent to tank through fuel bypass valve (10). More operation of fuel priming pump (2) will pull fuel from fuel tank (6) until the fuel lines, fuel filter (13) and fuel injection pump housing (17) are full of fuel. Do this until the flow of fuel from fuel bypass valve (10) is free of air bubbles.

Fuel Injection Pumps

A. Fuel Injection Pump uses a reverse flow check valve (RFC).

B. Fuel Injection Pump uses an orificed delivery valve (ODV).

C. Fuel Injection Pump also has an orificed delivery valve (ODV).

D. Fuel Injection Pump uses an orificed reverse flow check (ORFC).

Operation Of Fuel Injection Pumps

The main components of a fuel injection pump in the sleeve metering fuel system are barrel (A), plunger (B), and sleeve (D). Plunger (B) moves up and down inside the barrel (A) and sleeve (D). Barrel (A) is stationary while sleeve (D) is moved up and down on plunger (B) to make a change in the amount of fuel for injection.

Fuel Injection Sequence
(1,2,3) Injection stroke (positions) of a fuel injection pump. (4) Injection pump camshaft. (A) Barrel. (B) Plunger. (C) Fuel inlet. (D) Sleeve. (E) Fuel outlet. (F) Lifter.

When the engine is running, fuel under pressure from the fuel transfer pump goes in the center of plunger (B) through fuel inlet (C) during the down stroke of plunger (B). Fuel can not go through fuel outlet (E) at this time because it is stopped by sleeve (D), (see position 1).

Fuel injection starts (see position 2) when plunger (B) is lifted up in barrel (A) enough to close fuel inlet (C). There is an increase in fuel pressure above plunger (B), when the plunger is lifted by camshaft (4). The fuel above plunger (B) is injected into the engine cylinder.

Injection will stop (see position 3) when fuel outlet (E) is lifted above the top edge of sleeve (D) by camshaft (4). This movement lets the fuel that is above, and in, plunger (B) go through fuel outlet (E) and return to the fuel injection pump housing.

When the sleeve (D) is raised on plunger (B), fuel outlet (E) is covered for a longer time, causing more fuel to be injected in the engine cylinders. If sleeve (D) is low on plunger (B), fuel outlet (E) is covered for a shorter time, causing less fuel to be injected.

SMFS Pressure Relief To Tank

SMFS Pressure Relief To Tank
(1) Pressure relief to tank valve. (2) Spring.

Some sleeve metering fuel systems feature a pressure relief to tank valve (1) and spring (2) located under the torque control cover. The purpose of this feature is to maintain cooler gallery fuel by avoiding the fuel heating associated with recirculating excess fuel continuously back to the transfer pump inlet. Instead all excess gallery fuel is returned to the fuel tank. The return to tank flow also sweeps wear particles out of the fuel gallery. This configuration has the pressure relief to tank valve (1) located in an upper counterbore of the timing pin hole. A syphon break passage connects the gallery to the pressure relief passage. One half of the return to tank fuel leaves the gallery through the syphon break passage; the rest passes through the camshaft journal bearing to enter the bottom of the timing pin hole and pressure relief valve. An overpressure vent feature has been added to this configuration to protect the SMFS from failure in the unlikely event that the return to tank line should become blocked. This overpressure vent is located in the fuel inlet flange. The check valve used to bypass the transfer pump during priming pump gallery fill has been mounted on a nylon seat. The valve is held against the seat by a spring. Normally the check valve allows flow only into the gallery. In the event of gallery overpressure the check valve assembly lifts from its seat to prevent fuel back to the transfer pump inlet supply. The pump will function at increased gallery pressure to allow emergency operation, however, lip seal overload will greatly shorten the life of the seals. In addition the pump will overheat. Excess fuel pressure readings should be investigated to prevent premature fuel injection pump failure.

SMFS And HSMFS Differences

SMFS And HSMFS Differences
(1) Fuel air ratio control (FARC). (2) Sleeve control lever assembly (HSMFS). (3) Sleeve control lever assembly (SMFS). (4) Sleeve (HSMFS). (5) Sleeve (SMFS).

Sleeve Control Lever Assembly (HSMFS)
(2) Sleeve control lever assembly (HSMFS). (6) Pin (split).

The above split view shows the conventional SMFS sleeve metering control linkage on the right half. The HSMFS control linkage, shown on the left. The SMFS there are four sleeve control lever assemblies (3) on each control shaft. The HSMFS has two sleeve control lever assemblies (2) per control shaft. Each HSMFS sleeve control lever assembly indexes two fuel pump assemblies as it comes in between the two fuel pumps and indexes the two sleeves (4). Notice the amount of material on either side of the groove in the sleeve (HSMFS) (4). It is of equal thickness on either sides of the groove (sleeve wall thickness), while the thickness of the material on the sleeve (SMFS) (5) is thinner on the top than that on the bottom.

The SMFS design has sleeve control lever assemblies (4) in line with the fuel pump assemblies. Limited space between the control shaft and the fuel pump assembly limits plunger size and sleeve wall thickness. The larger 9 mm (.35 in) plunger is associated with thin sleeve walls. The HSMFS, shown on the left, overcomes this disadvantage by moving the sleeve control lever assembly (1) between two fuel pump assemblies to control two fuel pump assemblies at once. The sleeve control lever assembly (2) contains a pin (6) which is split in half. In this way it can be positioned between the two fuel pump assemblies to index the two sleeves (4). This arrangement allows the sleeve walls to be thicker and more capable of operating at the higher pressures needed for emissions control. The Fuel Air Ratio Control (FARC) (1) operates without piston preload when used with the HSMFS.

Operation Of Fuel Injection Nozzle (7000 Series)

The fuel injection nozzle goes through the cylinder head into the combustion chamber. The fuel injection pump sends fuel with high pressure to the fuel injection nozzle where the fuel is made into a fine spray for good combustion.

Fuel Injection Nozzle
(1) Carbon dam. (2) Seal. (3) Spring. (4) Passage. (5) Inlet passage. (6) Orifice. (7) Valve. (8) Diameter.

Seal (2) goes against the cylinder head and prevents leakage of compression from the cylinder. Carbon dam (1) keeps carbon out of the bore in the cylinder head for the fuel injection nozzle.

Fuel with high pressure from the fuel injection pump goes into inlet passage (5). Fuel then goes into passage (4) to the area below diameter (8) of valve (7). When the pressure of the fuel that pushes against diameter (8) becomes greater than the force of spring (3), valve (7) lifts up. When valve (7) lifts, the tip of the valve comes off of the nozzle seat and the fuel will go through the four orifices (6) into the combustion chamber.

The injection of fuel continues until the pressure of fuel against diameter (8) becomes less than the force of spring (3). With less pressure against diameter (8), spring (3) pushes valve (7) against the nozzle seat and stops the flow of fuel to the combustion chamber.

Operation Of Fuel Injection Nozzle (Pencil Type)

Pencil Type Fuel Injection Nozzle
(1) Cap. (2) Lift adjustment screw. (3) Pressure adjustment screw. (4) Locknut (for adjustment screw). (5) O-ring seal. (6) Fuel inlet. (7) Compression seal. (8) Valve. (9) Nozzle orifices. (10) Locknut (for lift adjustment screw). (11) Nozzle body. (12) Carbon dam. (13) Nozzle tip.

The fuel inlet (6) and nozzle tip (13) are parts of the nozzle body (11). Valve (8) is held in position by spring force. Force of the spring is controlled by pressure adjustment screw (3). Locknut (4) holds pressure adjustment screw (3) in position. The lift of valve (8) is controlled by lift adjustment screw (2). Locknut (10) holds lift adjustment screw (2) in position. Compression seal (7) goes on the nozzle body (11).

Compression seal (7) goes against the fitting of fuel inlet (6) and prevents the leakage of compression from the cylinder. Carbon dam (12), at the lower end of the nozzle body (11), prevents the deposit of carbon in the bore of the cylinder head.

Fuel, under high pressure from the fuel injection pump goes through the hole in fuel inlet (6). The fuel then goes around valve (8), fills the inside of the nozzle body (11) and pushes against the valve guide. When the force made by the pressure of the fuel is more than the force of the spring, valve (8) will lift. When valve (8) lifts, fuel under high pressure will go through the nozzle orifices (9) into the cylinder. When the fuel is sent to the cylinder, the force made by the pressure of the fuel in the nozzle body will become less. The force of the spring will then be more than the force of the pressure of the fuel in the nozzle body. Valve (8) will move to the closed position.

Valve (8) is a close fit with the inside of nozzle tip (13), this makes a positive seal for the valve.

When the fuel is sent to the cylinder, a very small quantity of fuel will leak by the valve guide. This fuel gives lubrication to the moving parts of the fuel injection nozzle.

Water Separator

Water Separator
(1) Vent valve. (2) Drain valve.

Some engines have a water separator. The water separator is installed between the fuel tank and the rest of the fuel system. For efficiency in the action of the water separator the fuel flow must come directly from the fuel tank and through the water separator. This is because the action of going through a pump or valves before the water separator lowers the efficiency of the water separator.

The water separator can remove 95 percent of the water in a fuel flow of up to 125 liter/hr (33 gph) if the concentration of the water in the fuel is 10 percent or less. It is important to check the water level in the water separator frequently. The maximum amount of water which the water separator can hold is 0.4 liter (0.8 pt). At this point the water fills the glass to 3/4 full. Do not let the water separator exceed this water volume before draining

Drain the water from the water separator every day or when the water level gets to 1/2 full. This gives the system protection from water in the fuel. If the fuel has a high concentration of water, or if the flow rate of fuel through the water separator is high, the water separator fills with water faster and must be drained more often. To drain the water separator, open drain valve (2) in the drain line and vent valve (1) at the top of the water separator. Let the water drain until it is all out of the water separator. Close both valves.

Governor

Cross Section Of Fuel System
(1) Lever. (2) Governor housing. (3) Load stop pin. (4) Cover. (5) Sleeve control shafts (two). (6) Inside fuel passage. (7) Fuel injection pump housing. (8) Drive gear for fuel transfer pump. (9) Lever (governor shaft). (10) Dashpot governor piston. (11) Dashpot governor spring. (12) Governor springs. (13) Spring seat. (14) Overfueling spring. (15) Thrust collar. (16) Load stop lever. (17) Carrier and governor weights. (18) Sleeve levers. (19) Camshaft. (20) Fuel transfer pump. (E.) Orifice for dashpot.