Water pressure system

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Revolver
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Water pressure system

Postby Revolver » Wed Aug 03, 2016 8:10 pm

Hey everyone, here's probably a simple one.

Old water pump (piston pump) blew up so installed a new one.
The pressure switch, factory set to 20/40psi, keeps on bouncing and bouncing causing cycling and eventually the breaker trips.
Pump is primed, delivers water when running.

Before operating I checked the pressure tank pressure and made sure it was at ~18psi.
But the pressure switch still keeps bouncing on off on off etc. trip.
My gut is telling me the bladder is the tank is probably also damaged.

Would you agree with my thoughts?

The height difference between the pump and tank is only about 8-10ft in a 3/4" pipe, so what ~5 or less psi there say...
Any info with your experience, thoughts?

After checks and checks I cheated and held the contacts for a moment to build some pressure, the system had running water for a few minutes and then once P dropped the switch was bouncing again the same.

Set up downstairs:
IMG_20160803_191130.jpg

Revolver
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Re: Water pressure system

Postby Revolver » Wed Aug 03, 2016 8:12 pm

Also what crossed my mind was the switch is installed right after the pump... But the last pump had the pressure switch installed right after the pump and before it died... It... Wasn't dead for a while and worked fine haha

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JollyJack
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Re: Water pressure system

Postby JollyJack » Wed Aug 03, 2016 9:11 pm

There should be 2 adjustments on that type of pressure switch, cut off and dead band. Check the "dead band" setting on the pressure switch. It's the difference between cut out pressure and cut in pressure. If cut out is 18 PSI and the dead band is zero, the pump will start as soon as it stops. If the dead band is 5, it won't start until the pressure drops to 13 PSI.

Alternatively, get some air into the hydrophore tank.
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Revolver
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Re: Water pressure system

Postby Revolver » Wed Aug 03, 2016 10:12 pm

Air in the hydrophore - 18psi (set when no water in it)
Cut in 20psi
Cut out 40psi

There are two adjustments: 1) cut in/cut out and 2) cut out.
Maybe I'll jump up the cut out a bit, take measurements of original set up and then play around and experiment. (But like I mentioned, the settings are factory supposed to be factory set, and it's brand spankin new...)

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Merlyn
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Re: Water pressure system

Postby Merlyn » Thu Aug 04, 2016 12:01 am

Got an accumulator in the circuit?
Did one back along and the bladder diaphragm mounded in the accumulator had a pin hole in it .
Put a pressure gauge in line and pumped up the scrader valve to 1.5 to 2.0 bar as per makers settings.
This valve is same as what you have in your vehicle tyres.
Note for any pressure drop when pumped up overnight.
The diagram/ bladder obviously cushions the pumped supply thus removing any psi fluctuations.
Sometimes if it's on the smaller side you can use your old pushbike pump.
By pumping up the system I noted that it raised the psi in the sealed system so if that's what it is you may well have to adjust that after repairs.
Worked for me.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Merlyn
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Re: Water pressure system

Postby Merlyn » Thu Aug 04, 2016 12:32 am

Just realised, do you call an accumulator a hydrophore over in Canada?
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D Winsor
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Re: Water pressure system

Postby D Winsor » Thu Aug 04, 2016 3:35 am

From the photo I noticed that there is something missing in the line from the pump to the Accumulator, Hydrophore or pressure tank before the pressure switch, namely some sort of check valve. With no check valve in the line the pressure switch will only sense the pressure built up in the discharge line when the pump is running which drops off quickly when the pump stops, not the stored pressure in the pressure tank.
As you said the original pump was a piston type pump so there would have been a check valve similar to a compressor discharge valve in the discharge chamber thus eliminating the requirement for an extra check valve in the discharge line. A failed discharge valve in the piston pump could also have been the cause of the pump failure.
Another good indicator would be if you can see the pump or motor shaft it would start spinning backwards when the pump stops. This would explain the loss of pressure on the system and the pump motor tripping out as water is flowing backwards through the pump.
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Revolver
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Re: Water pressure system

Postby Revolver » Thu Aug 04, 2016 6:44 am

Good eye D, in the pic the check valve isn't seen, it's about 4 feet before the suction valve and seems to be operational, not stuck & stops water.

The hydrophore is a smaller one that can be pumped with a bike pump, yup. And that's what I adjusted after the repairs.
Yeah I think I'd like to have a pressure gauge in the line so I can keep a closer eye though...

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D Winsor
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Re: Water pressure system

Postby D Winsor » Thu Aug 04, 2016 7:35 am

It is good that there is a check valve in the suction but the purpose of that valve in a suction line is to act as "Foot" valve helping to keep the pump primed but not necessarily to control the back pressure on the pump. As I mentioned in my previous post the discharge valve in the piston pump would have acted as a discharge check valve helping to maintain a constant pressure on the pressure switch. So I would not put too much faith in the suction line check valve.
Putting a check valve in the discharge line will defiantly work better for you, if for no other reason it will allow the pressure to falloff and equalize with the suction head in the pump while stopped so the pump is not starting under a higher than normal back pressure.
I say this because every pressurized water system I have come across with a centrifugal pump or pumps has either a Screw Down Non-return valve on the discharge of the pump or a check valve in the discharge line to the Hyrophore
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

Curt233
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Re: Water pressure system

Postby Curt233 » Thu Aug 04, 2016 8:30 am

I believe the bladder tank pressure should be the same as the cut in pressure. I would put a check valve on the discharge side before the pressure switch, like was stated earlier. Pump the bladder up to 2 psi, charge the system, then see how fast it drops. If it's still dropping rapidly, the bladder in the tank most likely has a rip in it and needs to be replaced.

Curt233
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Re: Water pressure system

Postby Curt233 » Thu Aug 04, 2016 8:31 am

Sorry 20 psi.

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Big Pete
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Re: Water pressure system

Postby Big Pete » Fri Aug 05, 2016 12:42 am

The short cycling is certainly a classic symptom of lack of air in the Hydrophore/ Pneupress tank.
Reading this I would like to point out the reason you want to add air to the bladder is to inflate it to its full size, so you may have to drain some of the water out before putting air in. So long as the bladder is expanding or contracting freely the air pressure inside the bladder and the water pressure outside will be the same and you have no way of telling what the volume of the bladder is. If the air pressure is slightly higher than the water pressure you know that the bladder must be full, and the air pressure is elastically stretching the bladder. Conversely, if the air pressure in the bladder is LESS than the water pressure you know that the bladder is squashed flatter than a pancake, either way you know it is not leaking.
Unfortunately, if you drained all the water out of the Hydrophore and pumped up the bladder to 18 psi you would probably burst the bladder!!

So stop the pump and slowly let the water go up to the accommodation, or run a tap somewhere, and keep adding air to maintain the bladder air pressure at 18 psi, when the water pressure falls below 18 psi you have the right volume of air, at the right pressure, inside the bladder and you can make fast the air filling line and switch the pump back to auto, oh and better shut that tap you were running. Everything is then set up correctly.

If you do not have a compressed air line with a pressure gauge for charging the bladder, the easy way is to drain the water out and inflate the bladder to its full size. Remember that if the bladder is full of air at Atmospheric Pressure then at 10 bar it will be compressed to 1/10 of its original volume! However do not put 10 bar air pressure on the bladder without a balancing water pressure on it!! Ideally you want the bladder fully expanded at or just below the pressure at which the pump cuts in. This will give the maximum quantity of water that can be delivered before the pump cuts in again. Reducing wear on the pump, motor and starter.

That tallies with your 18 psi air pressure in the bladder, 20 psi cut in, 40 psi cut out, so long as your gauges are accurate and the gauge lines are not blocked that should be fine.

As previously mentioned, an efficient non return or clack valve should be fitted in the pump discharge line.

With the reciprocating pump an accumulator vessel would have been fitted either as part of the pump or immediately after it to reduce pressure pulsations in the line. Usually the reciprocating pumps had a little "snifter cock" on the suction side that drew in air to keep this accumulator charged with air. (any surplus air was discharged with the water flow. This prevented pressure pulsations which would damage the pump and pipeline.

Another possible cause of short cycling could be pressure pulses in the pipe line, the pump starting could cause a pressure pulse to be transmitted down the pipe line and the pulse could be large enough to operate the pressure switch, these pressure pulses can also be reflected from tight bends etc so that there can be a whole series of them as a result of starting or stopping a pump. I notice several 90 degree bends after the pump. The simplest cure for this is to increase the length and reduce the diameter of the pipe between the pressure switch and the pump discharge pipe. Alternatively, connect the pressure switch to the Hydrophore tank itself, or to the Hydrophore OUTLET pipe. Or fit a pulsation damping valve similar to the ones used on Pressure gauges which are initially opened fully, resulting in big oscillations of the pressure reading and then slowly throttled in until the needle just trembles slightly, but that is difficult to do unless you have a pressure gauge next to the switch, and if the throttling valve became choked then the pressure switch would not work. Alternatively, rather than just damping the pressure pulses at the switch you could fit an accumulator between the pump and the switch, as in the old reciprocating pumps, that would stop any pressure pulses damaging the pump and pipes as well.

Another possible cause could be if the new pump had far too great a capacity causing a big pressure drop between the pump and the hydrophore, so the pressure at the pump would be almost immediately high enough to stop the pump, before the pressure in the Hydrophore had risen.

One ship I sailed on, the Kommandor Subsea, built by North Sea Shipyards in Denmark, had a very clever system, The tank did not have a bladder but a direct air/water interface. A level switch was fitted 1/3 below the top of the tank and a pressure switch mounted on the top. When the pressure fell to the cut in point the pressure switch sent power to the level switch, if the level switch was "UP" that in turn energised a solenoid valve that admitted air to the tank. If the level switch was "Down" it energised the starting coil for the water pump. Never seen that system before or since, but very clever, and very simple.

Hope some of this helps someone.

BP
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Big Pete
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Re: Water pressure system

Postby Big Pete » Tue Aug 16, 2016 7:43 am

HI REVOLVER,
Are you still following the thread you started?
Have you solved the problem yet?
What did you find?

BP
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Revolver
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Re: Water pressure system

Postby Revolver » Fri Aug 19, 2016 5:45 pm

Haven't been online in a while.
Now that I'm reading your post, I had actually done just that. I basically said to myself I'm going to reset and start from scratch to make sure I've done everything i can to ensure that it SHOULD work haha.
So it's been working now consistently since then, I have kept an eye on it while the pump is running and it chatters some but an acceptable amount of bouncing a pressure switch will do; ~3-5 seconds with of clicks and it stops at pressure.

I appreciate the help and advice you've posted guys. The more information the better.

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Merlyn
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Re: Water pressure system

Postby Merlyn » Sat Aug 20, 2016 3:02 am

Fluctuation free flow for the foreseeable forever future featured frequently from now on. ( hopefully )
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.


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