New Pressure Governor Works With Diesel Engines

New Pressure Governor Works With Diesel Engines

Apparatus Maintenance

During the past year, technical advances have been made in equipment and component design by manufacturers in response to needs expressed at seminars and conferences by fire department officials. One of the new component designs, now in production, is a fire pump pressure control governor. While fire pump pressure control governors are not new in the fire service, there are several features possessed by this governor design that contribute to relief from some of the current problems. These features are:

  1. The pump pressure governor works equally well on gasoline or diesel-powered pumpers.
  2. The pump operator, after setting the governor at the desired discharge pressure for minimum flow (one line, booster or IK inch, is sufficient) is free for assignment to other duty. The governor automatically increases the engine throttle for such additional discharge lines as may be required. The governor acts to reduce the throttle again if any of the added lines are shut.
  3. The governor automatically disengages the throttle control, allowing the engine throttle to return to idle speed if the water supply to the fire pump becomes insufficient to meet the discharge volume requirements. This prevents a runaway of engine and pump if the water supply is lost.
  4. The governor, in combination with an automatic control that shuts down the engine if oil pressure is lost or an automatic control that shuts off the engine if the engine cooling system overheats, provides a degree of operating safety never before available.

How governor works: The system of governor control is best understood by the schematic diagrams that illustrate the units of the system and their functions.

Figure 1. Schematic diagram of semiautomatic pump pressure governor. Fire pump operating at desired discharge pressure before activating governor system.

Figure 1 is a diagram of the pressure governor system before being put into operation. With the pump operating at the desired discharge pressure (from 90 to 300 psi) and at least a small volume of discharge to keep the water in the pump housing from overheating, the governor shutoff valve can be opened.

With the governor shutoff valve open, the control valve on the pump control panel is pressurized and water under pressure enters one end of the governor cylinder to move the piston to the lowest throttle position (Figure 2).

Figure 2. Water flow in system when shut-off valve is opened to admit water at pressure from the fire pump.

Reference pressure set up: Next, the control valve on the pump panel is moved from the OFF to the SET position. This setting permits water flow to the reference pressure reservoir, reference pressure gage and reference end of the governor cylinder (Figure 3). The control valve remains in the SET position only until the reference pressure gage reading is the same as the pump discharge pressure gage.

Figure 3. Governor control valve opened to SET position charges reference pressure system.

As soon as the pressures are in agreement, the control valve on the pump panel is moved to the RUN position and the engine throttle is moved to the closed, or idle, position. The pressure governor is now in automatic control (Figure 4).

Figure 4. Moving governor control valve to RUN position activates automatic system pressure control through governor clutch to engine throttle.

Moving the control valve to the RUN position cuts off pump discharge pressure to the reference pressure reservoir and to the reference end of the governor cylinder. It opens the line for pump pressure to act through the control valve to the governor clutch. The governor clutch is now locked up with the throttle, which is now controlled by movement of the governor cylinder piston. The piston has pump discharge pressure on one side and reference pressure on the other side. Any change in the pressure moves the piston to balance the pressure and this movement is transmitted to the engine throttle.

Fittings must be tight: The basic function of the major parts of the system will be ensured by proper maintenance. This maintenance is primarily to ensure tight fittings without any air leak. The function of the governor cylinder is to transmit lineal motion of the piston, as it balances pressures, to the engine throttle linkage. This requires quick and controlled movement with a minimum of friction. The piston has a Teflon seal to provide a low friction, which must also be preserved in the seals at each end of the governor cylinder.

The hydraulic clutch which engages the throttle control with the linkage from the governor cylinder is the operating heart of the system. The clutch is designed to hold engagement, once set, for the entire pressure range of 90 to 300 psi. Should cavitation or complete loss of water supply occur even momentarily to drop discharge pressure to 50 psi, the clutch will disengage and the engine will return to idle speed.

The clutch is spring-loaded to disengage completely when not pressurized. This allows free movement of the throttle arm during vehicle operation or pump operation prior to placing the pump pressure governor in operation.

A low friction thrust washer is used on each side of the disk pack to permit the throttle and governor cylinder levers to rotate around the clutch shaft when the clutch is engaged.

Trapped air acts as spring: The reference pressure reservoir is essential to store water from the fire pump discharge at the desired pressure, which is trapped between the air at the top of the reservoir and the reference side of the governor cylinder. The air trapped at the top of the reservoir acts as a spring or cushion to impart movement to the balancing piston.

A slow response to maintain the set pressure when one or more discharge gates are opened or closed indicates dirt or corrosion is present in the system. Care must be exercised in cleaning the governor cylinder or control valve and housing to prevent scratches from coarse abrasives. Such scratches will result in some loss of sensitivity of response to pressure change. A silicone type of light waterproof grease should be used in the control valve. The Teflon seal on the piston and at the end seals should not require a lubricant, which will pick up dust and dirt.

A strainer is provided in the line from the fire pump to the governor control valve and cylinder. This strainer should be cleaned monthly to insure continued satisfactory operation.

Technical data through the courtesy of American LaFrance.


No posts to display