THE VOLUNTEERS CORNER
PUMP FAILURE is probably the most difficult thing to rectify in a fire fighting operation. It takes so much time to replace a pumper that the entire fire attack can be compromised. What’s more, this is the type of failure that is sure to bring the severest criticism to a department because it is so obvious to the public.
Despite the importance of pumper reliability, it is surprising how many times I’ve found volunteer departments that have no schedule for testing pumps. This has sometimes been revealed when an engine has failed to draft during a training session. It takes but a few minutes to determine whether a pump is tight enough to draft from a reasonable height. This can be done right outside the firehouse.
In making a vacuum test, first attach two lengths of suction hose to an inlet, cap all the others and make sure that all hose gates, bleeders and drains are closed tightly. Also make certain that the booster tank drop valve is shut. Then begin priming. It doesn’t matter whether you start with a dry or wet pump. When the compound gage shows at least 20 inches of mercury, disengage the priming pump or other priming system. Then wait.
If the pump compound gage does not show a drop to about 12 inches of mercury in less than 10 minutes, the pump is in good condition for drafting.
A loss of vacuum greater than this indicates a leak somewhere in the “plumbing system” of the truck which should be identified and repaired. The leak often can be eliminated by tightening up the pump packing. However, make sure that a few drops of water are allowed to pass through the packing because this is the way the pump shaft is kept cool. If no water passes through the packing, you can quickly burn out the packing and possibly score the shaft. When this happens, it will be difficult to keep any packing in good condition.
If you’re in a hurry, it is not necessary to attach the lengths of hard suction. The reason for doing so is to test the suction hose for air leakage at the same time you test the pump.
When the source of the air leak is not apparent, shut off the motor after developing some vacuum. Then go around the truck and listen. Sometimes you can hear the passage of air at the trouble spot.
If you still can’t locate the leak, hook up the pumper to a hydrant. Then you can see the water leak under hydrant pressure. If you don’t have hydrants, run a supply line from another pumper and feed about 50 to 60 psi to the pump being checked. You can then crawl around underneath the truck without getting entangled with moving drive shafts. There is no need to use excessively high pressure, which has been known to do more damage than good.
Once a year it is profitable to put every pumper through the annual test. Actually, this is no more than a thumbnail acceptance test.
After the pump has been running a few minutes to give both engine and pump time to warm up, pump at rated capacity at 150 psi for 20 minutes. Then pump at 70 percent of capacity at 200 psi for 10 minutes and at 50 percent of capacity at 250 psi for 10 minutes. These figures are for Class A pumpers. Class B pumpers would pump at 50 percent of capacity at 200 psi and onethird capacity at 250 psi. A spurt test for a few minutes at capacity at 165 psi is recommended.
When you pump at the various pressures, note the revolutions per minutes and compare them with past records of the pump. If these are not available, check them with the record on the Underwriters plate stating the capacity of the pump and the truck manufacturer s test figures.
In determining the rpm, you shouldn t trust the tachometer. Check this instrument as well as the pump by using a revolution counter, which can be purchased in most hardware stores, and a watch with a large second hand—preferably a stop watch.
Alongside most Underwriters tack (tachometer) cable ends you will usually find the figures 1/10 or 1/2. This means that the tack reading obtained with a revolution counter should be multiplied by 10 or 2 to get the true rpm of the pump.
Tack readings that are higher than records of other years indicate the deterioration of the pump efficiency. If the rpm is excessively high, it indicates the need for pump overhaul or a slipping clutch.
If this test is made annually, you get a good picture of how a pumper is weathering the years. This may become a potent argument for replacing an aging pumper. It is the type of concrete evidence that town fathers find difficult to refute.