How does a pressure governor actually work?
There are several types of pressure governors, only one of which remains today. We could go into lengthy description of the old mechanical balance type, but will save that for the old-timers gatherings. First we must understand that the modern pressure governor is not a relief valve. The pressure governor is controlled by a very complex electronic computer, which patches into the engine Electronic Control Unit (ECU). The ECU has a feature called the cruise control, much the same as on your car. Whether you have active cruise control on your fire apparatus or not, the cruise control system is imbedded in the ECU. The pressure governor is married to the ECU. The pressure governor has two sides to the control function, that of RPM Mode and PRESSURE mode.
If you choose RPM Mode, you have control of RPM, but not pressure. If you select PRESSURE mode, you have control of the master pump pressure, but not RPM. When PRESSURE mode is selected, the pressure governor ties to the ECU cruise control and raises and lowers the RPM to control output pressure. It does so by placing pressure transducers in the pressure and suction sides of the pump, the system then reads the transducer outputs in speed counts — a calculation of speed is calculated in pressure readouts.
Consider that if the pressure governor is set at a selected pressure and another line is added and opened, the pressure will drop. The pressure governor sees the drop in pressure as a drop in speed and the cruise control increases the amount of fuel injected into the motor to bring it back to the preset pressure/speed. There are many more functions that can be accessed via the pressure governor systems. The simplest way to describe the pressure governor is to say that it is the cruise control of pressure monitoring.
What’s the difference in wear pads and roller blocks on an aerial?
Wear pads are the means whereby a product is placed on the aerial that sections slide upon during extension and retractions. The slide pad material utilized is chosen by the design engineer for the type and material of aerial being produced. Some are lubricated some are not. The roller system is one that utilizes a roller instead of a wear pad to accomplish low friction operations. However, some of the older rollers were made of aluminum or bronze and flattened out on the roller where the helix of the roller made contact with the beam and pounded it out during road travel. The result was flat rollers. One company utilizes a combination roller/pad system in a four-roller system. Today, the use of materials for the rollers and wear pads is a man made product and has a very long life if properly inspected and maintained.
What is the difference in chain drive versus gear driven pumps?
In a gear driven pump the power source providing rotation into the pump gearbox travels to the pump shaft through the selection of gears which increases pump input shaft rotation speed. In the chain drive pump the input shaft speed increase is accomplished through the use of an input gear to pump gear speed increase through a single high velocity (HyVo) chain. The end result is the same regardless of which type of system is used.
Can you explain how a two-stage pump works?
Certainly. Consider the two-stage pump as two single stage pumps married back to back. It has two single stage impellors on a common shaft, considered to be separated, by two separate cavities and is considered a series pump. When in operation, water enters the first impellor eye and is expelled out and into the eye of the second impellor. The volume of the first impellor is the maximum volume that the pump can supply. The first volume enters the second impellor eye and the PRESSURE is doubled and the flow remains the same as provided by the first impellor. You can use an electrical circuit to see how this works. Consider you have two 12-volt batteries connected in series. The final voltage will be 24 volts. Pumps can be more than two stages.
Do we need to have DOT inspections as well as state inspections?
In the fire service, depending on the state or province you operate, it makes a difference how the inspection process is mandated. DOT inspections are a mandate that the chassis and components are inspected and certified to pass at least annually.
Most states and provinces mirror what is required at the national level. NFPA stipulates that the frequency of inspection of critical components be carried out at least annually and that maintenance be performed to meet the manufacturers specifications, whichever comes first, but must not exceed annually. The inspections to which you refer are a stipulation of your local governing agencies.
What are some different auxiliary braking systems?
Auxiliary or addenda brake systems (AKA Retarders) are a requirement of heavier apparatus. Your Uncle Ernie suggests and recommends utilizing a means of auxiliary or addenda braking for all apparatus that can be retrofitted or outfitted at the factory with the devices. The end result is to create a retardation of wheel rotation and minimize the need to utilize the brakes, with increases the life of the brake components. The retarder is required to activate the brake lights when active and is recommended by the manufacturers to be shut off in inclement weather situations.
The inclement weather recommendation is a two-part equation: 1) shut off the retarder and 2) slow down. The retarder systems are also connected to the modern day “ABS” (Anti-lock Brake System) to prevent wheel lockup and spinout. The most common types of retarders are:
- Engine Compression retarder (AKA Jake Brake)
- Eddy current retarder (AKA Telma Retarder) utilizing electrical current and opposing pole shoes to create drag in the driveline.
- Hydraulic paddlewheel retarder, either integral with the automatic transmission or external in the driveline for manual transmissions (AKA Allison retarder)
- Exhaust Brake, which is a butterfly valve installed in the exhaust system — downstream from the turbo if so equipped — and block off the flow of exhaust to create high backpressure in the engine cylinders.
- Variable pitch turbocharger vanes that can close off the exit of exhaust from the engine, which creates the same effect as the exhaust brake listed in item (d) above.
How should I back flush my fire pump?
If memory serves me, I may have answered this in the past. But, depending on your location, you may not be able to perform tasks that others deem inappropriate during these times of extreme drought, like that currently ongoing in the West. Use these simple suggestions if you are permitted to perform a pump back flush. First, why are you back flushing the pump? Do you have some indication that there is a need for the back flush and what is it? Rocks induced into the pump? Sand in the pump? Maybe a noted decrease in pump flow during the annual pump test with a low negative inlet pressure at draft, which might indicate a restriction of flow through the impellor? If there is no perceived indication of a back flush, I see no need to perform the task.
If you are going to perform the task, make it a part of your monthly flush of the tank. You will be hooked to the hydrant anyway. If you have a hydrant of sufficient volume and pressure to perform the task, it will require no separate pumper to back flush your pump. You may leave the master suction screens in place or remove. I like to leave them in to see if I get any debris caught behind the screen or debris knocks the screen out.
- Close the tank suction and refill valves
- Remove all caps from inlets and one discharge outlet of the pump.
- Connect a hose from the hydrant or other pumper to the chosen discharge outlet
- Open the discharge to which you connected the hose.
- Begin the full flow through the inlet and out through the master suction connections. The pump shaft may turn backwards.
- If you have a two-stage pump, move the transfer valve from Volume-to-Pressure mode and back a couple of times while flowing water from discharge to suction.
- Remove the discharge hose, cap all connections and open the tank suction and crack the refill line.
- Evacuate the tank and refill. Evacuate the tank and refill a second time.
- Shut down and prep for readiness.
- Changing the water regularly can assist with the minimization of electrolysis within the pump system.