pressure problem with pump

[lake ainslie14]

You I have a jet pump and bladder tank.
the water pressure is fine when I open a tap. then psi lowers and pump comes on when it reaches 30 psi. but it cannot get back to 50 psi. the pump keeps running as long as the tap is turned on. as soon as you shut the tap the pump gets the psi back to 50 psi and shuts off

 

[John.g]

What is a jet pump and bladder tank?. Is it a negative head pump with a small pressure vessel mounted on top, if so, the pressure drops when you open a tap, the pump starts and will continue to run until the tap is shut and the flow switch detects no flow.

 

[lake ainslie14]

What is a jet pump and bladder tank?. Is it a negative head pump with a small pressure vessel mounted on top, if so, the pressure drops when you open a tap, the pump starts and will continue to run until the tap is shut and the flow switch detects no flow.

you are not familiar with jet pumps? . I have a well with a jet pump and pressure tank in basement. the pressure turns the pump on when get below 30 psi and shuts the pump off when it gets to 50 psi even when the water is running. now it will not reach 50 psi with the water running, that is the problem

 

[Deleted member 123817]

Maybe partial filter blockage? Presume water usage is less than the pump's rated capacity, does it reach 50 psi if usage is throttled in?.

 

[ShaunCorbs]

Is the bladder set correctly ie hasn’t lost its charge ?

 

[lake ainslie14]

Is the bladder set correctly ie hasn’t lost its charge ?

yes I charged the bladder " pressure tank". it was down about 10 psi. but after charging. it is still doing the same thing. I am baffled is it the pump or the bladder tank

 

[John.g]

Is this "pressure tank" ~ 20 litres or so?. or is it part of a bigger storage tank?.
If its a multistage pump then maybe hole in one of the diffusers, you may be able to reduce the cut out pressure by 5 psi or so.

If you can give a reasonable estimate of the pressure vessel size and the pre pressure and time how long it takes to rise from 30 to 50 psi (with no water demand) I can tell you what the pump output is which may help.

 

[lake ainslie14]

Is this "pressure tank" ~ 20 litres or so?. or is it part of a bigger storage tank?.
If its a multistage pump then maybe hole in one of the diffusers, you may be able to reduce the cut out pressure by 5 psi or so.

If you can give a reasonable estimate of the pressure vessel size and the pre pressure and time how long it takes to rise from 30 to 50 psi (with no water demand) I can tell you what the pump output is which may help.

there is only one 20 gallon tank. it only takes a few minutes once the tap is shut to reach 50 psi and shut of. but can never get above 30 once tap is open

 

[Deleted member 123817]

This would indicate that it's pumping - 50/60 LPM in filling the tank. If the pressure stays at 30psi even with the tap just cracked open then that indicates to me that the pump is variable speed and controls the pressure to 30 psi until no demand and then rises to 50psi and cut out.

 

[Deleted member 123817]

Should have said pumping - 20/30 LPM .

 

[lake ainslie14]

But this pump and tank worked perfectly fine for a number of year and the pressure would rise even with the tap on, it would rise to 50 psi with the tap open.

 

[John.g]

Does the 30 psi change at all if you vary the flow rate from the tap?

 

[lake ainslie14]

No it does no not. This problem just started. I am trying to decide if is the pressure tank or the pump. Before I buy one

 

[John.g]

Before you do anything just think about these points.

You have a 20 gall?? (91 litre) pressure vessel.
This will take in 28 litres of water in rising in pressure from 30psi to 50psi (if precharged to 30psi) and will release the same amount, 28 litres, when the pressure falls from 50psi to 30psi.
Assume the pump is a fixed speed pump pumping 30LPM.
You open a tap to give a flow rate of 10LPM.
The pressure vessel will supply 28 litres of water in 2.8 minutes in falling from 50psi to 30psi, the pump then starts and will supply the 10 LPM to the tap, the remaining 20LPM will recharge and raise the pressure vessel from 30psi to 50psi in 1.4 minutes. The only way with a fixed speed pump that the pressure can stay at exactly 30psi is if the tap flowrate is exactly the same as the pump capacity, 30LPM.
The only technical reason that I can think of is that the pump is a variable speed unit, maybe for some reason it was set to 100% output for years and something has changed the setting?.

Have you any details or links to this pump and its controls?

Why is it a problem for you if the pump (now) runs at a constant 30psi or 2bar?

I can't see the pressure vessel being a problem, if it has a membrane and is holed then the pump will start immediately as soon as any tap is opened but you would have noticed this. If the precharge pressure is 0 psi for some reason or other then the pressure vessel will only supply 10 litres of water resulting in the pump starting/stopping more frequently.

Pump problem? its supplying the required flowrate at a constant 30psi and then cuts out at 50psi when demand is over.

Anyway once you establish as to whether its on fixed or variable speed will narrow down your search for a solution.