Voltage at pump is 120 & air pressure in tank 24 psi Grundfos MQ3-45 Pump cuts out (Stops) then immediately restarts every 10 seconds insted of continuous running when there is demand for water
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The 34 psi of the pressure tank sounds high, but it depends on what the cut-in pressure is set at in the pump pressure switch. Typically the pressure switch is for 20-40 psi or 30-50 psi. To establish what the pre-charge of tank should be , you need to establish what the pressure switch setting are (i.e 20 - 40 psi , etc.) Run the water and watch the pressure gauge and note at what pressure the pump comes on. The pressure tank needs to be pre charged 2 -4 psi below that cut-in pressure. So if the cut-in pressure is say 30 psi, then the tank needs to be pre charged to 28 psi.
To pre charge the pressure tank, turn the pump off. Drain the pressure tank of water to relieve all pressure in the tank. Then check the pressure of the tank at the air valve. Set the pressure to 2 psi below what the cut-in pressure is.
If you adjust the pressure switch, say from 20-40 to 30-50, you will need to go through the procedure of re adjusting the pressure in the tank. I hope this helps....
Mine did that. Little known that the Grundfos MQ pump has a small pressure tank on the end. If the pressure is low and the air volume is therefore low, then any tiny loss of water results in pressure drop and pump cycles on. Check the pressure in the tank. This is not well described in the Grundfos service manual.
To pump up the pressure bladder: 1. remove the rear cylindrical cover (swift bash with a fist downwards) 2. unscrew plastic cap on the end (about 2 inches diameter with tapered sides 3. attach pump to schrader valve and pump up (22-25 psi according to service manual)
Reassemble.
Suggest teflon tape to schrader valve stem to try to create a secondary airtight seal.
Pressure is bleeding back through the pump or system to the tank or well or where ever the water is coming from. Should be some sort of one way valve to keep water from going back to the source, mounted somewhere so that once pressure is pumped up, it will hold that pressure in the part of the system that has the pressure switch that controls the pump.
That or you have a leak where you can't see it. (Actually you do, it is just internal and not leaking outside the pipes!)
if you have a pump for the whole house you need to check the bladder tank. there is a air valve on the top. Check the pressure with a tire gauge you should have at least 20 PSI this will stop the pump from the on and off thing.
You can compress air yuo can not compress water. thats why the ballder tank. As the pump work to shut off pressure it is compressing air. then when you use a little water the pump does not run until a large about is run then the pump will re fill the system
adjust your pressure switch on your compressor .remove the cap and turn the screw clockwise to increase and counterclockwise decrease.turn the screw counterclockwise a bit and release some air till the compressor start pumping.then just before to reach 120 psi turn counterclockwise to stop the compressor at 120.then release some air again till it cuts in again and look at what pressure it will stop.keep going that way till you get your 120 psi.cut in should be around 90 psi(30 psi differential)depending what kind of pump you have (if the pump can handle 150 psi )you can adjust it to cut in at 120 and cut off at 150 and install a pressure regulator adjusted to 115 to 120 and get a nice steady pressure going to your nail gun.(the best way to do it!!!)
The booster should have been placed after you restrooms with a check valve to prevent back-pressure. then you can adjust both the sub-pump pressure, and the booster pressure accordingly
let me know
You suspect this unit as being a two stage because of the unusually high cut off pressure. It is a single stage and the motor really has a difficult task and is being pushed to the limits. to reach this pressure. We usually reset the pressure to lower setting ~~ say around 140. Your pump probably has a leaking intank check valve (brass fitting at tank) or leaking valve plate in pump. Simple tests : with pressure in tank unplug compressor from outlet and listens for air leak around pressure switch. As you unplug the running compressor from outlet you should hear air leaking from pressure switch for just a moment as air is let out of airline from pump to tank. If air leaks out till zero pressure then change the valve. If tank holds pressure then valve probably ok. Next test, with no air in tank and air filter removed, plug in compressor and feel intake port for strong suction. If the valve plate is bad, suction will decrease as pressure neers the 120 mark till the point of feeling that air is actually blowing out of intake. With good valve plate there will be strong suction untill unit reaches set pressure. If valve plate is bad also change the cylinder and piston ring. Good luck with your repair.
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