Accumulator Seems Somewhat Redundant - ATM

[BargeeSpud]

Hiya,

 

Just filled up the water system on the new build & the accumulators (1 in hot & 1 in cold sides) appear to have no effect on the water pump, open a tap & the pump cuts in immediately. It also cuts out virtualy immediately you turn the tap off.

 

My accumulators are both set to 21PSI, my Jabsco 31395-0292 water pump switch is supposed to cut in at 15PSI & cut out at 25PSI, so I thought my accumulator pressures were right on the money. Yes, I did set the accumulator pressures with the pump off & a tap open so that there was no pressure in the system.

 

How can I set the system up so that the accumulators actually do what they're intended to do?

 

Cheers.

[LEO]

Hi,

 

It's worth checking carefully some Jabsco pump don't need accumulators.

 

L

[BargeeSpud]

Just had a thought since posting the question. Is it possible that an air lock could give the problem I'm experiencing? It's just that 1 accumulator is mounted on its side & the other is mounted with the water pipe entering at the top, so its possible that the accumulators don't have any water in them.

Hi,

 

It's worth checking carefully some Jabsco pump don't need accumulators.

 

L

Nothing in the pump's instructions to say that. Not that it isn't true of course, I'll look into it. Thanks. Edited May 4, 2015 by BargeeSpud

[Paul C]

WHEN did you set the accumulator, and how? If you turn off the water pump then open a tap until no more water comes out, then the water side of the diaphragm will be "empty" and the air side will be "at its maximum volume". If you have the taps closed and switch the water pump on (or open a tap until the pump comes on....if your accumulator is set up properly....) then the water pump runs, reaches pressure and switches off, before any taps are run the accumulator will then be "full" of water and "at its minimum volume".

 

Note I've used full/empty for the water side - water is incompressible, so a change in volume is reflected in its change in quantity of water in it. Pressure doesn't affect the volume, it will transmit the pressure evenly to all the internals of that particular run of water pipe/accumulator/pump outlet side/taps/ calorifier/inlet of PRV etc.

 

HOWEVER the change in volume of the air side of the accumulator WILL affect the pressure, in fact it will be directly related, according to the gas law of:

 

PV=nRT

 

P = pressure

V = volume

n = amount of gas

R = a constant

T = (absolute) temperature

 

So, given the amount of gas is constant, the temperature isn't varying massively, the more volume, the less pressure.

 

Basically you need to set the accumulator so that it correctly ranges from one side to the other.

The easiest way is to turn the pump off, open the taps, then set the air pressure in the accumulator to just above atmospheric pressure, ie pump a little bit of air in with a footpump/bicycle tyre pump. Then fill it with water (taps closed, let pump run then stop, don't run any more taps) and check the pressure and it will be pretty much the same as the pump's max pressure ie its cut out pressure.

 

Setting or measuring the pressure in an accumulator with an unknown amount of water/air in is meaningless in itself.

[BEngo]

As others have said first check you don't have a fancy pumps that controls flow without needing an accumulator.

 

For maximum benefit, the cold water accumulator pressure, with taps open, pump off, and no water flow should be set to the cut-in pressure of the water pump. According to the OP's this is about 15 psi, so the 21 psi he has set is too high.

 

To check the cut-in pressure, put some air in the accumulator- say 10 psi, with the pump off and all taps open, no water flowing. Switch the pump on and taps off, and wait until the pump stops. Set one tap to run slowly and wait until the pump cuts in. Immediately switch the pump and the tap off, (This may take a few goes to get dead right, but practise is cheap!) Then measure the air pressure in the accumulator. This is the cut in pressure. Open all the taps and wait till water stops flowing. Adjust the accumulator air pressure to the cut in pressure.

 

The hot water accumulator is only there to take up expansion as the water is heated, so anywhere between say 15 and 20 psi is OK.

 

 

N

[system 4-50]

In case it helps:

MPN: 31395-0292 Jabsco PAR-Max Water Pressure pumps have provided years of great service to many boaters. Now Jabsco has refined the product line with two pumps. The 1.9 GPM and 2.9 GPM (7 LPM and 11 LPM) are designed for vessels requiring a quiet, smooth flow, on-demand pump. These pumps feature a three chamber diaphragm design offering a smooth flow from .65 GPM to 2.9 GPM (2.5 LPM to 11 LPM), and come with a built-in Pulsation Eliminator to control unwanted cycling and noise. These performance characteristics match the needs of the typical vessel with up to three fixtures.

• Connections: for 13mm (½”) bore hose or Hep20 push-fit connectors CW193
• Dimensions: 230mm long, 152mm wide, 110mm high
• Fuse Size: 10 amp
• Maximum Current: 4.4 amp
• Output: 11 litres/minute (2.4 gallons/minute) open flow
• Pressure Switch: cuts in at 1.0bar (15psi) - cuts out at 1.7bar (25psi)
• Efficient, high-flow, self-priming pump serving 2 or more outlets
• Multi-diaphragm design self primes to 1.8m vertical lift, can run dry without damage
• Supplied with snap-in ports for hose or Hep20 connectors
• Quiet running
• Motor protected by automatic thermal overload cut-out

Edited May 4, 2015 by system 4-50

[Paul C]

 

In case it helps:

MPN: 31395-0292 Jabsco PAR-Max Water Pressure pumps have provided years of great service to many boaters. Now Jabsco has refined the product line with two pumps. The 1.9 GPM and 2.9 GPM (7 LPM and 11 LPM) are designed for vessels requiring a quiet, smooth flow, on-demand pump. These pumps feature a three chamber diaphragm design offering a smooth flow from .65 GPM to 2.9 GPM (2.5 LPM to 11 LPM), and come with a built-in Pulsation Eliminator to control unwanted cycling and noise. These performance characteristics match the needs of the typical vessel with up to three fixtures.

• Connections: for 13mm (½”) bore hose or Hep20 push-fit connectors CW193
• Dimensions: 230mm long, 152mm wide, 110mm high
• Fuse Size: 10 amp
• Maximum Current: 4.4 amp
• Output: 11 litres/minute (2.4 gallons/minute) open flow
• Pressure Switch: cuts in at 1.0bar (15psi) - cuts out at 1.7bar (25psi)
• Efficient, high-flow, self-priming pump serving 2 or more outlets
• Multi-diaphragm design self primes to 1.8m vertical lift, can run dry without damage
• Supplied with snap-in ports for hose or Hep20 connectors
• Quiet running
• Motor protected by automatic thermal overload cut-out

 

 

Is the built in pulsation eliminator - a small accumulator? (Would only need to be small, combined with its variable speed operation).

Edited May 4, 2015 by Paul C

[BargeeSpud]

Well, according to the Jabsco site there is no need for an accumulator. Bad advice from the guy fitting the water system - again; I should have known. Oh well, I've got them fitted now, so I'll try setting their pressures to the cut in of 15PSI & see what happens. If no difference, I can remove them & sell them.

[Tony Brooks]

Before doing much more please check that the accumulator in the hot system is just that, an accumulator. I think it is supposed to be an expansion vessel. Now, specially to confuse the unwary both are the same thing except the pressures are different. The expansion vessel is set close to the pump cut out pressure (tap open, pump off) and its job is to allow expanding water somewhere to go without raising the pressure unduly. Some calorifier manufacturers actually demand one.

 

The accumulator on the cold side is normally set to about the pump cut in pressure (tap open, pump off).

 

I think the Jabsco pumps that claim not to need an accumulator fall into two types. An expensive one with electronic motor speed control that is governed by system pressure so as the pressure rises to cut out the motor slows down. A cheaper one with an inbuilt prv that is set to a little below pump cut out pressure so as the pressure rises towards the cut out the valve opens and vents excess deliver back to the inlet side so the pump keeps running.

 

If the water flow from the tap is greater than the maximum pump delivery (litres per min.) then the pump will not cycle or cut out whatever you set the accumulator to.

[frangar]

Set the one on the cold side to about 12 psi and the one on the hot side to about 27psi.

 

If they have been fitted in the right place the cold one will act as an accumulator and the one on the hot side will act as an expansion vessel....basically the same bit of kit doing different jobs....

 

the accumulator stores water under pressure from the pump meaning the pump doesn't cut in if a small amount of water is drawn off...but the pump will run on once the tap has been closed to build the store back up again.

 

The expansion vessel on the hot side allows the water in the calorifier to expand when heated so reducing stress in the calorifier and hopefully stopping the pressure relief valve from dribbling.

 

Cheers

 

Gareth

[PaulD]

Well, according to the Jabsco site there is no need for an accumulator. Bad advice from the guy fitting the water system - again; I should have known. Oh well, I've got them fitted now, so I'll try setting their pressures to the cut in of 15PSI & see what happens. If no difference, I can remove them & sell them.

I had a problem with vibration / hammering eventually tracked down to an airlock above the calorifier. I remember now why I put a bleed valve in there! When I rang Jabsco for advice they said that I should have an accumulator installed and the claims in the advertising only apply to people who don't have any problems !!!???

 

Paul

[BargeeSpud]

Some great info coming out which I'm going to follow. The hot accumulator being an expansion vessel is obvious when you think about it, so I'll reset that one to the figures suggested & the cold one to the pump's cut in. Can't do anything for a couple of days now, but when I do, I'll post the results.

 

Cheers for now.

[steve hayes]

On my build the accumulator didn't work as you described, couldn't understand why it wasn't working.

With the pump turned on and at pressure, I let all of the air out go the accumulator but to my surprise the pump didn't kick in, I would have expected some water to have been needed.

I removed the accumulator to investigate, no problem water came freely out if the Tee. On investigation I noticed the diaphragm was pushed up to the opening and would not budge. I pushed it firmly back with a bar and heard crackling sounds as it came free from the opening. I refitted and setup as normal and it worked as expected. Ten years on its still working.

[BargeeSpud]

On my build the accumulator didn't work as you described, couldn't understand why it wasn't working.

With the pump turned on and at pressure, I let all of the air out go the accumulator but to my surprise the pump didn't kick in, I would have expected some water to have been needed.

I removed the accumulator to investigate, no problem water came freely out if the Tee. On investigation I noticed the diaphragm was pushed up to the opening and would not budge. I pushed it firmly back with a bar and heard crackling sounds as it came free from the opening. I refitted and setup as normal and it worked as expected. Ten years on its still working.

 

Thanks for that, something simple to check out if all this fiddling with pressure settings doesn't work.

 

Cheers.