Relay Pumping Operations

C. Putting Relay into Operation

  1. Operation always begins with source pumper

  2. Largest capacity pumper used at source

  3. If relay being supplied from draft, source pumper have to develop higher net pump discharge

      pressure than other pumpers in relay

  4. Higher net pump discharge pressure needed because relay pumpers will have residual pressure at

      intake to reduce amount of pressure needed from pump

  5. Important to remember that maximum capacity of relay determined by capacity of smallest pump

      and smallest hoseline used

  6. Once water supply established, source pumper opens uncapped discharge or allows water to

      waste through dump line until first relay pumper ready for water

  7. Failure to keep water through pump could result in loss of prime

  8. Discharge pressure built up to desired value by increasing throttle

  9. Dump line discharge valve slowly closed to keep from wasting all water from water supply

  10. Relay pumper waiting for water with dump line or discharge open and pump out of gear

  11. When both source pumper and relay pumper ready, discharge supplying hoseline on source 

        pumper opened while valve on dump line closed in coordinated action

  12. Discharge to supply line opened slowly to prevent sudden discharge into empty hoseline

  13. Water begins to move from source pumper to relay pumper

  14. As water fills line, air forced through pump and out open dump line of relay pumper

  15. When water comes out of dump line, pump on relay pumper engaged

  16. Another option to start relay, or at least fill hoselines, with water from apparatus water tank

  17. Works best on short relays using 3-incbh hose

  18. On long lays of LDH, may not be possible to completely fill hose between two pumpers

  19. Most desirable to maintain intake pressure of 20 to 30 psi

  20. If relay pumper receiving intake pressure greater than 50 psi, valve to dump line on relay pumper

        adjusted to limit residual to 50 psi maximum

  21. Pump discharge pressure increases as throttle setting on relay pumper increased; therefore, valve

       to dump line gated down to maintain 50 psi residual pressure

  22. If dump line allowed to flow unrestricted, friction loss would increase in hoseline from source

        pumper to point pump would go into cavitation

  23. Once pump discharge pressure on relay pumper reached desired pressure with water being

       discharged, portion of relay established and no further adjustments necessary

  24. When next relay pumper ready for water, same procedure followed

  25. First relay pumper opens discharge valve supplying next pumper while closing dump line on

        coordinated basis

  26. Next relay pumper allows water to discharge through dump line and follows same procedure used

        by first relay pumper receiving water from source pumper

  27. When water reaches attack pumper, operator bleed out air from supply line by opening bleeder

        valve on intake being used

  28. Intake valve on attack pumper opened and water supply established through relay

  29. When one attack line shut down, operator opens dump line to allow water to flow and prevent

        dangerous pressure buildup in relay

D. Operating the Relay

  1. Once relay in operation and water moving, pump operators set automatic pressure control devices

  2. Use of automatic pressure control devices essential when operating in relay due to cumulative

      nature of pressure increases when changes in flow occur

  3. Auxiliary cooler adjusted as necessary to maintain proper engine operating temperature over

      extended periods of time

  4. If pumper equipped with intake relief valve put in service

  5. If valve adjustable, set to discharge at 10 psi above static pressure of water system attached to or

     10 psi above discharge pressure of previous pumper in relay

  6. At no time should relief valve be set for higher amount than safe working pressure of hose