Accumulator bafflement

[Crazy-Diamond]

I have had an elderly accumulator on my boat. An 8 L Cleghorn. Every now and again I have had to re-pressurise it but recently I could not pump any air in at all, so I decided it was time for a new one.

When I removed the old one it was very heavy. It was totally full of water, so the membrane must have split and explains why I could not pressurise it with air.
I fitted a new one and I cannot work out why it is not working. It does not seem to be pressurising at all.

There are no valves in the system like one-way valves and every stop is open. When I open a tap water runs freely and the pump pumps.

As soon as I close the tap the pump stops running.

I have tried with the accumulator pressurised to one bar. I have tried with two bar and even higher. When the accumulator was pressurised to 2 bar I tried opening a tap without the system powered up and no water came out.

I disconnected the pipe to the accumulator with the system powered up and water came out.

What I’m expecting to see is that once the pump has switched off (at pressure) I can then open a tap without the pump kicking in immediately. But what I am saying is exactly the same as when the old accumulator was full of water. The pump turns on whenever the tap is opened, and turns off whenever the tap is closed.

The pump is less than six months old, a Whale jobby. All of the plumbing is also new so I can’t think of something else in the system that is causing this.

Any ideas would be very welcome at this stage




Sent from my phone

 

[Boater Sam]

Are you pressurising the accumulator with the pump off and a tap open? You should be.

 

[Crazy-Diamond]

Yes, I’ve done the setup with the system depressurised. I cannot work out how there can be pressure in the accumulator but nothing coming out of the taps

 

[neilf39]

How accurate is your pressure gauge? If you pumped it up higher than the pressure your pump is delivering it won't do anything. It needs to be just below your pump delivery pressure so it starts to fill and then as this compresses the air it will hopefully equalise before it completely fills. Perhaps the pump is not as powerful as it used to be.

 

[VicS]

Any ideas would be very welcome at this stage

When supplied there was plug in the inlet connection to keep critters out.

You have not removed the plug,

.

 

[vyv_cox]

This is the method I have used for years, not requiring a gauge. Release any air from the accumulator. Turn on a tap. Note the rapid and continuous cycling of the water pump. Begin to pump air into the accumulator. The cycling of the water pump will reduce, with increasingly longer pauses between activation. As more air is introduced the pauses will reduce in duration. Stop pumping air and release a little air until the pause length is maximised. Job done.

 

[Iliade]

If your pump is set to a lower pressure than the accumulator it will not displace the membrane and will thus behave as if the accumulator is not fitted.

[edit crossed post with Vye ^]

 

[Crazy-Diamond]

I think the issue was caused by having a crappy foot pump with equally crappy gauge which was under-reading. I used a digital air pressure gauge this morning, using a method similar to Vyv's suggestion. I think the unit was over pressured, but this does not explain why it was not pushing water out when the pump was not running. This morning when I powered the boat up the pump started to run as if it was finally pressuring the accumulator. As I let out air the characteristics you'd hope for started to happen, and the pump would not kick in straight away. It seems as if setting an accumulator is more done by feel than by accurate measurements!

 

[Bilgediver]

I think the issue was caused by having a crappy foot pump with equally crappy gauge which was under-reading. I used a digital air pressure gauge this morning, using a method similar to Vyv's suggestion. I think the unit was over pressured, but this does not explain why it was not pushing water out when the pump was not running. This morning when I powered the boat up the pump started to run as if it was finally pressuring the accumulator. As I let out air the characteristics you'd hope for started to happen, and the pump would not kick in straight away. It seems as if setting an accumulator is more done by feel than by accurate measurements!

You are correct in what you say and the setting point depends on what pressure your pump can achieve. As others have tried to point out , you were initially over pressurising your accumulator to the extent that the pump could not move the diaphragm so the accumulator was doing nothing and might as well have not been there. As you reduced the accumulator pressure the pump was able to push water into it until the pressure equalised. By doing the routing outlined by Vyv you should have established the point where the accumulator is at its optimum pressure when at rest for your system this will be a relatively low pressure compared to what you might expect. It is wrong to pump an accumulator up to a pressure close to operating pressure when there is no water pressure in the system as the pump may not be able to overcome the accumulator pressure which seems to have been happening in your case. I hope you got a big one Size matters.

 

[Boater Sam]

I think the issue was caused by having a crappy foot pump with equally crappy gauge which was under-reading. I used a digital air pressure gauge this morning, using a method similar to Vyv's suggestion. I think the unit was over pressured, but this does not explain why it was not pushing water out when the pump was not running. This morning when I powered the boat up the pump started to run as if it was finally pressuring the accumulator. As I let out air the characteristics you'd hope for started to happen, and the pump would not kick in straight away. It seems as if setting an accumulator is more done by feel than by accurate measurements!

I found the easiest way to get the correct pressure is to over pressure the accumulator first, Let the pump run then close the taps, let it run till it stops and slowly reduce the pressure by pressing the valve until the pump just kicks in again.