Smokerr
Mechanical
- Mar 28, 2010
- 14
I am in the process of setting a procedure for dealing with whats probably a fairly typical situation but I can find no information on it in regards to what occurs at the low end of the tank water levels.
We have a 29 foot supply in the tank with an intake thats 3 feet with an Anti Vortex plate on top of that. Somewhere around 3 feet we will of course loose suction. The question is how far above 3 feet would that occur (I am currently using 5 feet as the critical point as at full flow that allows about a minute worth of options)
Basis for the Concern:
Our fire pumps use heat exchanger and the cooling is per a discharge tap off the supply side.
Once the discharge pressure goes away, the pumps will self destruct due to lack of cooling, i.e. the engines will seize and then things will start to break. I suspect engine will come apart and possibly couplers and a lot of inertia back into the engine from the pump rotating assembly (3500 gpm pumps at 100% so its a pretty large mass)
Despite redundant pumps no provisions were made to for a pump shutdown with the loss of cooling (high engine temperature would be an easy one to use). No low tank level shutdown of any type either.
Once the engines fail, anyone in the pump room is at risk.
5 feet is probably safe but has anyone tested a system down to the Anti Vortex plate level and is 4 feet more likely a safe value?
I don't currently know if the procedure will allow manual shutdown of the pumps prior to destruction.
The procedure does have an increasing level of reporting that we are getting critical as the tank level gets lower as well as instructions to evacuate at 5 feet currently if not ordered to shut them down.
Tank makeup water system does not have the refill capacity to maintain or even significantly assist the situation in a multi zone fire (manual bypass is part of the procedure to help as much as possible and becomes irrelevant by the time 3 pumps are running at 100%)
We have a 29 foot supply in the tank with an intake thats 3 feet with an Anti Vortex plate on top of that. Somewhere around 3 feet we will of course loose suction. The question is how far above 3 feet would that occur (I am currently using 5 feet as the critical point as at full flow that allows about a minute worth of options)
Basis for the Concern:
Our fire pumps use heat exchanger and the cooling is per a discharge tap off the supply side.
Once the discharge pressure goes away, the pumps will self destruct due to lack of cooling, i.e. the engines will seize and then things will start to break. I suspect engine will come apart and possibly couplers and a lot of inertia back into the engine from the pump rotating assembly (3500 gpm pumps at 100% so its a pretty large mass)
Despite redundant pumps no provisions were made to for a pump shutdown with the loss of cooling (high engine temperature would be an easy one to use). No low tank level shutdown of any type either.
Once the engines fail, anyone in the pump room is at risk.
5 feet is probably safe but has anyone tested a system down to the Anti Vortex plate level and is 4 feet more likely a safe value?
I don't currently know if the procedure will allow manual shutdown of the pumps prior to destruction.
The procedure does have an increasing level of reporting that we are getting critical as the tank level gets lower as well as instructions to evacuate at 5 feet currently if not ordered to shut them down.
Tank makeup water system does not have the refill capacity to maintain or even significantly assist the situation in a multi zone fire (manual bypass is part of the procedure to help as much as possible and becomes irrelevant by the time 3 pumps are running at 100%)