Chp 12 Flashcards
Relay operation
Using 2 or more pumpers to move water over a long distance by operating them in series
Water supply pumper
Takes water from hydrant or static source and pressurizes to next apparatus
Should be biggest pumper
aka Source pumper
Relay pumper
Receive water from a pumper and pressurize to the next one
Can be smaller as it can rely on previous pumper
Fire attack pumper
At the fire scene
Supplies the attack lines
Hose tender
Carries a mile or more of LDH
May also have a pump to help in the relay
Have wide assortment of valves and manifolds
LDH is split between attack and supply
Note
Relay pumping considerations
Sole source of water or just augmenting?
Length of the lay. If more flow is needed:
Diameter or number of hoses increase
PDP increase (may not fix problem, pumps give best volume at 150 psi, higher reduces volume), also consider hose capacity
More pumpers to overcome FL or elevation
Not practical to replace a line in place; use additional pumpers to create a second line
Can add pumpers to a line to operate at lower pressure
Putting a relay into operation
Put largest capacity pump at the source
Source throttles up and opens a discharge till next pumper is ready
Next has discharge open and pump out of gear
Source closes dump line at opens discharge at the same time to avoid losing prime
Bleed air out of dump line before opening intake valve via source pumper then put relay pump in gear
Maintain 20-30 psi residual
Operating the relay
Attack pumper sets pressure governor
Set intake relief valve of relay pumpers to 10 psi above static pressure or safe working pressure of hose
Ste attack pumper relief to 50-75 psi
Don’t try to correct for minor fluctuations
Shutting down the relay
Start at attack
Decrease throttle, open dump line valve and disengage pump
Mind water hammer
Open relay
Use dump tanks at each relay point
Relief valve
Either installed by mfg
Or external add on screwed on to the pump intake connection
Need bleeder cuz lots of air can cause loss of discharge pressure or water hammer
Inline relay valve
Allows late arriving pumpers to connect into an existing line and boost pressure/volume
LDH
Relay supply hose of 3.5” - 6”
Minimum pump capacities
Based on table pumping at 185 and 200 750 gpm pump: 250 and 500 gpm flow 1,250 pump: 750 flow 1,500 pump: 1,000 flow 1,750 pump: 1,250 flow
Equalize distance between pumpers as much as possible
Different diameter hose may be used but adjust distance and PDP to compensate
Overall capacity is determined by the smallest pump
Note
Some depts have relay task forces
Note
Supply lines used
If MDH of 2.5” or 3” lay multiple lines
If LDH of 4” or 5” usually just one line
Pushing air into the pump may cause water hammer
Note
Remember to close bleeder valve when drafting
Note
Late arriving pumpers
Initial line can be small and spaced apart
Inline relay valve is placed on supply
Late pumpers connect to it and boost pressure and volume
If supplying more than one attack pumper
Use a discharge manifold to break LDH into 2 or more lines to connect to different pumpers
Have one LKH inlet and a combo of MDH and LDH discharges
Relay relief valve
Placed along line to enhance safety and reduce possible damage to the pump
Pump efficiency
100% of capacity at 150 psi
70% at 200 psi
50% at 250 psi
at draft
If pressure governor
Attack pumper sets it to pressure to correct for cumulative pressure fluctuations along the line
