Short Cycling MQ 3-35

Users who are viewing this thread

raw915

New Member
Messages
1
Reaction score
0
Points
1
Location
Illinois
I have a submersible well pump that supplies water to two houses, one located about 30 feet higher in elevation than the other. Incoming pressure to the upper house varies between 20 and 40 psi, so I installed a Grundfos MQ 3-35 pump to boost the pressure to a maximum of 95 psi.

The system works but there is one problem for which I can see two possible solutions. The Grundfos pump is designed to turn on if the flow rate exceeds about 0.3 gpm or if the output pressure drops below around 29 psi. I have verified that there is virtually no leakage in all lines running from the pump's outlet. Typically the pump runs the pressure up to around 75-95 psi (when inlet pressure varies between 20-40 psi) and then shuts off. Then over a period of 15-30 minutes the outlet pressure gradually decreases to the inlet pressure. When the inlet pressure from the well-pump is below about 30 psi the Grundfos pump will run again.

I'm guessing that water is leaking back through the Grundfos pump and allowing its outlet pressure to drop to its inlet pressure. My next step would be to install the non-return valve into the Grundfos pump inlet line, which should prevent water from leaking back through the pump. But is that enough? The Grundfos pump contains a tiny internal pressure tank (13.5 oz), but would it also help reduce short cycling if I installed a small (say two-gallon) pressure tank at the pump's output?
 

Reach4

Well-Known Member
Messages
38,749
Reaction score
4,400
Points
113
Location
IL
http://www.freshwatersystems.com/support/L-MQ-TL-001.pdf

Page 8 says there is a built-in check valve. It seems to me that an extra pressure tank would reduce cycling significantly, whether that cycling is from a small leak in the check valve or a small drip in the house plumbing.

That extra pressure tank would not have to be installed near the pump. It could be somewhere in the house.
 
Last edited:
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks