Experimenting at Drills Helps Pump Operators Understand
The Volunteers Corner
There is one nice feature about training pump operators. They don’t have to rely on theory alone. They can operate according to department procedures and then try other ways on the drill ground to become convinced that the other ways are unsatisfactory.
One of the problems with training programs in busy departments is that the pump operator training sessions sometimes provide no time for letting the men see why certain operations do not work. To expand understanding, there is nothing like trying different things with pumps.
In teaching, I find that one of the most common misunderstandings about pumps Is the use of wyed lines and pressure control devices—relief valves or pressure governors.
Test layout: You can explain that a pressure control device will not protect wyed lines, but many men will remain doubtful until you show them on the drill ground. This can be done by taking at least four lengths of 2 1/2 hose off a pump and attaching a wye at the end. From each side of the wye, run a couple of lengths of 2 1/2-inch hose with nozzles of 200 gpm flow or more.
Operate the pump at the proper pressure (130 psi for 1-inch tips with 100 feet on the wyed lines and 200 feet of line from the pump to the wye) and set the pressure control. Note the engine pressure and take pitot gage readings at each tip. Then while taking a pitot gage reading at one tip, order the other tip shut down. The pitot gage will show an immediate and continued rise in pressure at the flowing tip.
The engine pressure remains the same, but the energy that was flowing water to both tips is now concentrated in flowing a larger gallonage to a single tip. The men at this tip now have too much pressure and a line that is difficult to handle.
Different size lines: Try this same experiment with one 2 1/2 and one 1 1/2-inch line off the wye. The increase in pressure at the tip will be far greater when the 2 1/2 line is shut down than when the 1 1/2-inch line is shut down because of the difference in gpm between the two lines when both were in operation.
To show that the failure of the pressure control device is based on the inability to sense the diversion of energy from one wyed line to the other, place the wye on a pump outlet and use two lines. The pressure control device will now work because the energy shift is close enough to the pump.
Use of eductors: Another problem area is the use of inline eductors. Why should you limit the length of 1 1/2inch foam lines to two lengths (at the most, three) beyond an inline eductor?
To show this, use two inline gages. You can buy special couplings for these gages or you can braze the bowls of a male and female coupling and tap a ¼-inch thread into the united coupling, for a gage. Place an inline gage on each end of the inline eductor and pump water at the usual pressures for educting foam concentrate.
The gage readings will be visual convinces of the large loss of pressure in the eductor as energy providing pressure at the eductor inlet is transformed to providing water velocity in the eductor. The result is a drop in pressure of at least 30 percent at the eductor outlet. That means that 150 psi coming into an inline eductor will be 100 psi or less going out the eductor. From this, you can see what you can expect in nozzle pressure with more than a couple of lengths of hose beyond the eductor.
Inline pumping: Pump operators may not really be convinced of the advantage of larger total waterways for feeder lines in inline pumping and the effect the lengths of feeder lines have on the volume of water received at the pump from the hydrant.
Stretch one line of two lengths of 2 1/2 hose from a hydrant to the pump. Take a line, and later lines, off the pump and flow enough water to bring the pump intake pressure to 20 psi. Take a pitot gage reading at the tip (or tips) to determine the gpm flowing.
Vary the feeder line layout by going to eight and 10 lengths of hose and then use parallel lines of 2 1/2 hose. Do the same thing with 3-inch and larger hose if you have it. Measurement of the flows each time with the suction intake (residual) pressure at 20 psi will be convincing.
If you have a large-volume hydrant, use a higher intake pressure as a constant