Relay Pump Operations: Who Says It's Just for the Long Lay?
Flow Test #3
The hydrant used for flow test #3 is a good example of a high volume system with what I would consider an average system pressure. The static pressure for this system was 60 psi, the hose evolution consisted of 350 feet of 4” LDH ATTACK HOSE with a maximum operating pressure of 275 psi and a AWG HRV.
Note: the system pressure dropped only 2 psi after flowing 910 GPM in the first hose lay. Again 910 GPM is a good start with emphasis on the word start. The HRV has little to no friction loss in the hydrant only mode, in fact, an additional test was conducted from hydrant pressure without a HRV and the results were the same.
The relay pump operation tests were conducted with and without the use of the HRV with very close results. The numbers speak for themselves. The increase obtained from the relay operation with the HRV over the hydrant lay was 490 GPM with a flow of 1400 GPM. The increase from the relay not using the HRV versus the one with the HRV was 75 GPM reaching a flow of 1475 GPM. There is not much of a gain in flow but compare the engine pressures of the two engines at the hydrants in the two relays.
The evolution using the HRV required an engine pressure of 275 psi to move 1400 GPM while the engine without the HRV had a much lower engine pressure of 195 psi while moving 75 more GPM. Reason being, the HRV being used had a high friction loss in the relay mode. Is this a problem? I say no. Granted the engine pressure was high but if that is what it takes with this HRV to get the required flow then so be it. It’s not a problem as long as the maximum operating pressures for all equipment being used are not exceeded.