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Relay Pump Operations: Who Says It's Just for the Long Lay?

Paul Shapiro

Flow Test #4

Flow test #4 involved the use of hydrant system that was good in all respects having a high volume and high system pressure (120 psi static). The supply line used was 300 feet of 4” LDH SUPPLY HOSE with a maximum operating pressure of 185 psi. Akron and Humat HRVs were also used. All flow tests were done three times, once using each of the HRVs and once without.

The single supply line supplied directly from hydrant pressure was able to deliver 1000 GPM to the pumper. As you can see, after flowing the 1000 GPM there was still a 100 psi hydrant residual pressure. This evolution was repeated two more times using the HRVs with fairly good results. The Akron valve lost 49 GPM with a flow of 951 GPM and a hydrant residual of 95 psi. The Humat lost 55 GPM reaching a flow of 945 GPM also with a hydrant residual of 95 psi. Both valves were considered to be worth the slight loss for the convenience they provided for the operation.

The second portion of the flow tests compared the relay pump operations using the HRVs to the relay operation that did not. The operation using the Akron HRV delivered a flow of 1610 GPM with a hydrant residual of 65 psi. That’s 659 GPM more than the straight hydrant lay gave us. The numbers for the Humat valve were higher moving 1830 GPM with a 50 psi hydrant residual.

The water way in the Humat valve set in the relay mode goes straight through with no bends while the Akron valve has one 90 degree bend, thus the difference in flows. Finally the relay was done without the use of the HRV producing the high flow for this series of tests which was 1856 GPM. There was still more water left in the hydrant which is noted by the 45 psi residual hydrant pressure. The stopping point for this operation was the hose. The maximum allowed operating pressure of 185 psi was reached. To take better advantage of this hydrant a second 4” relay line could have been stretched between the pumpers splitting the flow into two lines which would lower the engine pressure.