Submersible Pump Question

scott_vt · Oct 29, 2012

Carl_NH said:
Sorry - Dirtyoldman,

You are right for your pumps BUT wrong for a submersible, a sprinkler pump and a transfer pump on a fire truck are totally different setups than a submersible well pump. The above ground pumps CAN work without output for a while (3-5 minutes) and do not build a lot of pressure due to their design - single volute, single impeller setup.

Now submersible well pumps will build pressure and require some flow to stay cool. Most SUBMERSIBLE WATER WELL PUMP installations include a pressure relief valve alogn with the pressure switch that once that is exceeded it will start to bleed off water if the switch fails to stop the pump.

These pressuire relief valves are normally set at 70-80 PSI, as submersible well water pumps can generate 80-100PSI.

The pressure relief valves on submersible well pump systems allow some flow - usually around 1 GPM to prevent the pump from destroying itself.

Carl

Good Afternoon Carl,
Your right on the on fire dept pumps. Ive been a volunteer for almost 30 years, and when ever we have one of our engines in pump mode for more than a few minutes, if we are not flowing water, I usually recirculate the tank water through the pump. This keeps the pump housing, shaft packings etc cool, and prevents over heating. A simple thing to do rather than damage an expensive piece of equipment.

turnkey4099 · Oct 29, 2012

One on the heater, one on the tank is redundant. Both are on a common connection and the pressure (static) is the same throughout. I see no benefit at all in having two. Got a cite where such is required?

Harry K

Carl_NH · Oct 30, 2012

Harry,

You are correct - you dont need two, however they serve different purposes Temp & Pressure in the heater and pressure in the pump line. By code they need to be on the water heater and probably many dont have two devices in the house due to city water.

I'll stick with two as I can set the pump PRV to 20-30 PSI above the cutout pressure and solve the problem before creating a mess of water from the DHW heater or boiler. Those on the DHW T&P are typically not adjustable.

TheGoose · Oct 31, 2012

Not only will your pump and motor burn up if you let it run without flowing or pumping water but if you have PVC casing it could melt the casing directly around the pump and lock the pump/motor unit in place and ruin the well. I have seen this happen many times. If I ever encounter a situation where the possibility for shutting off flow from a submersible can happen like in irrigation systems I install some sort of bypass or minimum flow to idiot proof the system. For example, drill a small pilot hole through a shut-off valve so that it can never completely lose flow. You only need a few GPM of water flowing around the motor to keep it cool.

turnkey4099 · Oct 31, 2012

Okay, that makes some sense but I doubt your submersible would build enough pressure to open the heater PRV. Those type pumps have a max pressure and unless you have a commercial one it will be 100 psi or less no matter how long it runs.

Harry K