Drafting Problems Haunt Every Pump Operator
The Volunteers Corner
Drafting is the bane of a pump operator because some of the problems are beyond his immediate control on the fireground.
If a stream is too shallow to draft the volume of water required, digging a hole in the stream bed is the only answer—and a most unsatisfactory answer at that, particularly if the stream has the descriptive name of Stony Brook. If there is an air leak in the “plumbing system” of the pumper, there isn’t much the operator can do about it during a fire. That’s not the time to conduct a vacuum test to spot the source of trouble.
However, there are some things that a knowledgeable pump operator can do to turn an initial drafting failure into success.
Inability to prime: Before starting to operate the priming device, note the position of the pump compound (vacuum) gage needle. Its normal position when the pump is not being used may be either side of the zero and only by noting this will you be able to tell whether you are pulling some vacuum. ‘ Failure of the gage needle to move normally toward the vacuum side while operating the priming device indicates that there is an air leak somewhere in the system.
In my experience, air leaks are the most common cause of priming failure—or failure to maintain a prime.
The suction hose couplings should be tightened firmly. Changing the gaskets whenever they show a groove or when they start to harden will help make an effective air seal when the couplings are tightened. If both the male and female couplings have long handles and the gaskets are in good condition, two men can make up the couplings tightly without the use of a rubber hammer, which is often used to tighten suction hose couplings.
Before starting to prime, make certain that all hose gates and gated suction inlets (except for the one you may be using) are closed. Except for those with hose attached, all hose gates and suction inlets should be capped as an added precaution against air leaks into the pumper’s plumbing system.
Pump packing: A common air leak source is the pump packing. If water sprays from the pump packing, then the packing is much too loose and must be tightened until, as at least one pump manufacturer recommends, a minimum of 10 drops of water a minute comes from the packing. Personally, I don’t like to tighten packing beyond the point where a continuous succession of drops—about one a second—come from the packing.
If the pump loses its prime, it may be because of an air leak. However, it also may be because you did not build up the pump pressure enough before opening the discharge gate for the first line. The laws of physics don’t have anything in them about hope, so don’t get into the situation where you can build pump pressure up to only 50 psi or so and hope that you can increase the pressure as you charge the line. Get a proper prime so that you can raise the pump pressure to about 100 psi before trying to charge a line.
At this point, a common error is to open the discharge gate too rapidly. You should have one hand on the engine micrometer throttle and the other on the discharge gate and as you open the gate s-l-o-w-l-y, increase the engine speed with the throttle to maintain 100 psi on the pump.
Shallow water: If you have to draft large volumes of water, the end of the suction hose has to be at least 12 to 18 inches below the surface of the water. If you must draft in relatively shallow water, a pan-type strainer that has solid sheet metal toward the surface of the water is effective in preventing whirlpools that let air enter the suction hose.
Leaves, weeds and other debris—even duck feathers and mud—can clog a suction hose strainer and choke down the water supply. When this happens, the intake gage will show more than the number of inches of mercury that is normal for the drafting conditions. Sometimes a man can wade out to the strainer and clear it and at other times you can use a booster hose stream to wash away some of the debris or keep floating debris from nearing the strainer.
While keeping these drafting problems in mind, also keep an ear open to the sound of the priming pump, the main pump and the engine. There is nothing to be gained by continuing to pump when crippling damage to the pump or engine is imminent. Radio word to the fireground that you are going to have to shut down so that an unexpected stoppage of water won’t endanger a hose crew in a hot location in a building. a