Frequently Asked Questions

The impeller is the item within the pump that actually pumps the water. In a single-stage pump, there is one impeller. It has a double suction eye, which means it takes in water from both sides. It does this no matter how the pump is being supplied with water (tank, side suction, rear suction, etc.) For a two-stage pump, there are two impellers, each with one suction eye. When pumping in the “Volume” mode, each impeller is pumping 1/2 of the water, at the same time at the same pressure. The water is then discharged.

The alternate to “Volume” mode is called “Pressure.” In this mode, the first impeller pumps 100% of the water to a certain pressure; then, instead of the water being discharged, it is routed into the suction eye of the second impeller. Whatever pressure the first impeller pumped the water at, the second impeller will double it.

The option of pumping in “Volume” or “Pressure” is changed by the Transfer Valve. It moves the pump from one mode of operation to the other. Transfer valves, if not exercised regularly, are notorious for getting “stuck” in one mode or the amount of travel is limited, preventing a mode from being fully engaged. If it is “stuck” in the Volume mode, the pump should still be capable of pumping capacity (assuming there are no internal problems to the pump) but the ability to run a compliant NFPA pump test is lost due to not being able to make the full transition to Pressure. All departments with two-stage pumps should ensure they exercise the transfer valve back and forth weekly to prevent this.

As part of our Pump Maintenance w/ NFPA Pump Test program, we check the operation of the transfer valve. For more information on the program or pumps, please give us a call.

Note: In pump lingo, “Volume” is also referred to as “Parallel;” “Pressure” is also referred to as “Series.”

The main reason to test your pumps is for the peace of mind it gives knowing that the apparatus is fully functional and ready to handle a major incident. Additionally, a centrifugal fire pump is a mechanical device, just like your car. The very moment it is put into service, it is being worn out. By testing your apparatus annually, you have the ability of predicting your maintenance budget requirements 2 to 3 years in advance. This is possible with the exclusive FLSI graph. The graph can give you a visual indication of pump problems as they start growing year to year.

Here is an excerpt from NFPA standard 1911 -Appendix A: “Investigation has shown that where regular and systematic tests of pumps are not made, defects often exist and can continue undetected for considerable periods under light demands at ordinary fires; these defects only become apparent at a large fire where the pump is called on to perform at or near rated capacity.

Other reasons are that it is an NFPA recommendation, and ISO (Insurance Services Organization) gives your department the most points for 3 consecutive years of pump testing. While NFPA is only recommendations, if there were ever a problem, with the legal system as it is today, they would most probably be treated as law.”

NFPA recommends pump testing apparatus on an annual basis.

NFPA 1911 3.1* – “Frequency Service tests shall be conducted at least annually and whenever major repairs or modifications to the pump or any component of the apparatus that is used in pump operations have been made.”

This only stands to reason – testing is not only checking for pump efficiency, but also checking the engine and transmission as well. You may be thinking “We don’t use our trucks that much, would every other year be sufficient?” While certainly every other year is better than never, both NFPA and manufacturers recommend testing on an annual basis. Unfortunately, lack of use is as hard on a piece of equipment as abuse. With the rigors fire apparatus and pumps are put through, the results can change dramatically from year to year.

Some of the things little use can cause include:

  • Condensation in the pump transfer-case oil. Because it rarely gets brought up to operating temperature, this can start to form rust on bearings and other critical components.
  • Priming pump frozen up from lack of use – the primer oil gels with water causing the vanes to stick in the rotor, thereby making the primer inoperative.

Note: It has come to our attention that some insurance companies only require departments to test their pumps every other year. The fact that manufacturers recommend testing annually, NFPA states those manufacturer recommendations shall be considered minimum criteria. Also the ISO 1980 Fire Suppression Rating Schedule awards the most points for an average of a 1 year interval between the last 3 service tests.

Centrifugal fire pumps are closely fitted machined parts operating at high speeds. The average speed of a fire pump impeller is 4000 RPM at capacity. The impeller is spinning within what are called “seal rings.” These rings and the impeller run together with a .015 of an inch clearance. When the pump is run from draft, the water carries with it sand and other foreign material that gets in between these surfaces and wears on them, causing them to gradually get farther apart. As these tolerances get bigger, more water is bypassed internally in the pump, thus reducing its capacity. In this context, bypassed is referring to the water that is re-circulating within the pump, from discharge to suction. Because of this fact, pump capacity is reduced.

It should be noted that a large majority of fire departments do not operate their apparatus from draft, but all municipal water systems also contain sand, rust and other foreign materials not noticed while running your faucet or shower. These materials begin to show up when the large demands of a centrifugal fire pump are hooked to the system and begin operating.

Another form of wear often not noticed or understood is cavitation. Cavitation can cause severe damage to a centrifugal fire pump. Cavitation is caused by attempting to pump more water out of the apparatus than is being received.

An important note to remember, wear, due to sand or cavitation is cumulative. In other words, it progressively gets worse from additional use. The only way to correct this wear is to overhaul the pump.

Yes. Prior to NFPA 1911 – 1997 edition, this was not allowed. The 1997 edition has restored this alternative testing method of testing the pump from a positive pressure water source. Even with the restoration of the positive pressure pump test; it is FLSI’s recommendation to test fire pumps from draft.

The following is an explanation of why: The pump test is performed to check the efficiency and ability of all pump components, especially the ability to pull and hold a prime. The test results would have little meaning if they could not be compared to previous results. The most important comparison is the test performed at the apparatus factory by Underwriters Laboratory. The service test that FLSI performs is designed to mimic this test as closely as possible (with exception of duration.) The UL test is performed from draft, so the best way to compare results is to run the service test from draft.

This is usually a hot debate within an apparatus committee; should we stick with the traditional pump packing or should we specify mechanical seals?

Packing is by far the more traditional and more popular; however, some newer pump models are coming only with a mechanical seal. Packing is field adjustable and field replaceable. However, it requires effort to monitor the drip rate and performance. Then, it requires maintenance to adjust and/or replace when the situation calls for it. Provided the packing isn’t neglected for long periods of time, it is relatively inexpensive to replace.

Mechanical seals are “easier” on the front side and during pump performance. Just use the pump properly and don’t worry about the seal. However, when the seal is worn, the pump will leak excessively and a vacuum will no longer be possible until the seal is replaced. Additionally, they are much more expensive to replace than the packing, due to having to disassemble part of the pump. Because of this, it is very difficult to do in the field.

Another factor to consider is the quality of water in the community. Rural areas tend to have water that is harsher than municipal water supplies. The harsher the water, the more abuse taken by the packing or seal.

The answer to the debate is choosing your point of view – constant maintenance issue (packing) or a sudden failure one day (seal.)

Both of these items operate on the discharge side of the pump. Regardless of which option a department chooses, the objective of each is the same – protect firefighters from pressure surges that could cause them to lose their balance.

The traditional discharge relief valve offered by the pump manufacturers is a mechanical device that senses the pressure of the discharge water. If the pressure is too high, it opens and usually dumps the water to the suction side of the pump, thus lowering the pressure within the pump. While it is doing this, the engine and pump spin at a constant speed. Relief valves are less expensive to purchase up front and less expensive to maintain. They are relatively standard to repair, usually just needing to be rebuilt.

Engine governors operate on a different principle. Rather than operate the engine/pump at a constant speed and dump the excessive water to relieve the pressure, they fluctuate the speed of the engine/pump to maintain discharge pressure. Engine governors, while more expensive up front, usually incorporate a type of gauge package and throttle as well. When comparing up front costs, be sure to compare apples to apples. Being that the components are electronic, repair costs will vary, based on the severity of the issue.

On this issue, there is no answer other than use what will work best for your department.

We need some basic information on each of your vehicles. In the Publications & Downloads section, go to Forms and find our “Critical Vehicle Info.” This will guide you as to what information we need.
No, the program has been discontinued.