HOW TO AVOID FALSE READINGS AT THE PUMP PANEL

BY STEWART LOEB

For fire departments to be effective today, they must employ both innovation and tradition. They must avail themselves of modern technology as well as innovative firefighting procedures. New apparatus and tools and equipment provide us with efficient technology in the fight against fire. Tradition must also have a role, as it is invaluable in fighting fires in older buildings that are still prevalent in great numbers. Today we have modern pumpers that are diesel-powered and are highly efficient. Many fire departments have gone back to the solid bore nozzle. This traditional nozzle is operated at lower pressures, and many departments have found great success with it. However, using the traditional nozzle with the modern pumper has not been without problems. These problems are not insurmountable. Information and awareness are all that are needed to mix innovation and tradition successfully.

Say that a 125-year-old mercantile building is showing heavy fire on the first floor. The first-arriving engine company locates, tests, and hooks up to a nearby hydrant. Members stretch four 50-foot lengths of 2¾-inch hose to the front of the building. Water is started, and an outside attack has begun with a 2¾-inch line with a solid-bore nozzle equipped with a 11/8-inch tip.

The pump operator has to consider three factors when deciding how much pressure to put on this hoseline: the nozzle tip size, the length of the stretch, and from what elevation the nozzle will be operating.

ENGINE PRESSURE (EP) = NOZZLE PRESSURE (NP) + FRICTION LOSS (FL) + ELEVATION (EL)

Let’s assume, in this example, it is standard practice for this engine company to operate with 40 psi on the nozzle and members have given five psi for their friction loss per length. Since they are operating on ground level, elevation is not a factor in figuring out the correct engine pressure.

EP = 40 + 20 + 0 = 60 psi

The correct engine pressure would be only 60 psi. Yet modern pumpers, when hooked up to an adequate hydrant, will commonly deliver well over 150 psi at idle! What’s the pump operator to do? The solution is to “gate down” the discharge-that is, open the discharge handle only partially to deliver the proper pressure of 60 psi.

This is similar to the operation of your kitchen sink. You don’t turn on the faucet full force just to get a glass of water.

The pressure at the discharge gauge must be set with the nozzle open. In the above example, this was an easy task, as the nozzle was operating outside and in full view of the pump operator. Why must the pressure be set with the nozzle open? With the discharge gate only partially open and the nozzle shut, you will get a “false” reading once the hoseline fills with water. You will get a static pressure reading instead of a flow pressure reading. Once the proper pressure has been set with the nozzle open and the nozzle has been shut down, the discharge gauge will fluctuate, giving two different readings. With the nozzle open, you will get a true flow pressure reading. Once the nozzle is shut, you will get a false or static pressure reading. This does not occur when pumping a line with the discharge gate fully open.

If the pump operator is pumping 60 psi and then sees the needle of the discharge gauge jump to 150 psi, he should not attempt to readjust the pressure but should then consider that the nozzle is shut down, water is not flowing, and a false or static pressure reading is showing. A glance at the flow-meter will tell the pump operator if the nozzle is open when the nozzle team is operating out of sight of the pump operator. One can deduce that modern pumpers should be equipped with flowmeters at each discharge.

If the pump operator wrongly attempts to gate down further while the nozzle is shut down, he will be doing the nozzle members a great disservice. Once they open the nozzle, they will have inadequate pressure, and the needle of the discharge gauge will quickly drop to zero!

It is often necessary to gate down while pumping several lines from one pumper, as it is quite uncommon for all lines to require the same pressure. For example, if six lengths of 1¾-inch line are stretched for a fire in a lumber shed and a backup line of six lengths of 2¾-inch hose is stretched to the same point, their respective pressures will vary distinctly:

For 1¾-inch hose, EP = 50 + 120 + 0 = 170 psi.

For 2¾-inch hose, EP = 40 + 30 + 0 = 70 psi.

The pump operator will set the pump to deliver 170 psi to the 1¾-inch line and then only partially open the discharge gate to provide just 70 psi to the 2¾-inch line. The pressure reading for the 1¾-inch line, since the gate is fully open, will read a constant 170 psi whether the nozzle is open or closed. The pressure reading for the 2¾-inch hose will fluctuate between 70 psi when the nozzle is open and 170 psi when the nozzle is closed, giving a “false” or static pressure reading. The pump operator must remain aware that the nozzle is closed (glance at the flowmeter) and not attempt to gate down any further.

Pump operators must be keenly aware of what is happening not only at the pump but on the fire floor as well. They must monitor portable radio messages and watch the fire building for progress or problems among their many other tasks, often simultaneously.

STEWART LOEB is a lieutenant and 14-year veteran of the Fire Department of New York, assigned to Engine 65 in midtown Manhattan. He previously was a firefighter with the Atlanta (GA) Fire Department for five years.

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