Calorifer Pressure Woes

[Colecraft Sunflower]

Hi there. I have found evidence that the PRV on my calorifier is lifting regularly. So, I have replaced the PRV with a new one from the manufacturer of the calorifier so I know it is correctly rated (4 bar). After replacing it I turned on the water supply. The water pump kicked in but the new PRV lifted straight away. 
 

The valve released a small amount of water (about 4 tablespoons). Every time the water pump kicks in the PRV repeats this process. 
 

The water pump and accumulator is a Xylem CW425. Manufacturer literature says it cuts off at 1.7 bar.

 

Question: Why is this causing the PRV to lift?

 

Thank you in anticipation 🤗

[David Mack]

Have you checked the accumulator pressure?

[pearley]

In my case it was because the pressure switch fitted to the pump was faulty. Replaced it with an external Square D plus a guage so I could see what's happening.

[Tony Brooks]

20 minutes ago, pearley said:

In my case it was because the pressure switch fitted to the pump was faulty. Replaced it with an external Square D plus a guage so I could see what's happening.

 

or try turning the pump pressure setting down. Usually a screw in the end of the pump rather than the motor. It might work for a while so you have time to get the switch @pearley recommended.

[Colecraft Sunflower]

Thanks guys. I foolishly presumed the pump / accumulator pressure was factory set and not adjustable so I didn’t even consider this. Instead I was focused on the consequence rather than the cause. I’ll check this out 👍.

[Tony Brooks]

Unless the accumulator has lost all its pressure I doubt that will be the cause. If it has then a wtaer hammer like episode upon turning a tap off could well cause  those symptoms. A 4 bar PRV should give plenty of headroom for a 3 or 3.5 bar pump to avoid than. Hence I suspect it is pump pressure,

[Iain_S]

2 hours ago, Colecraft Sunflower said:

Thanks guys. I foolishly presumed the pump / accumulator pressure was factory set and not adjustable so I didn’t even consider this. Instead I was focused on the consequence rather than the cause. I’ll check this out 👍.

Any time I've bought an accumulator, it's been charged to a pretty high pressure. I think the last one was at 80p.s.i.

 

 

[blackrose]

I don't understand how accumulator pressure can exceed a pump's cut-out pressure? Isn't the maximum pressure of a system dictated by the cut-out pressure of the pump?

 

I guess I'm assuming the accumulator is correctly set at a few psi below the pump's cut-in pressure.

Edited September 29, 2024 by blackrose

[Onewheeler]

2 minutes ago, blackrose said:

I don't understand how accumulator pressure can exceed a pump's cut-out pressure? Isn't the maximum pressure of a system dictated by the cut-out pressure of the pump?

If the accumulator is pumped up higher than the pump outlet pressure it won't do anything and might as well not be there.

[blackrose]

1 minute ago, Onewheeler said:

If the accumulator is pumped up higher than the pump outlet pressure it won't do anything and might as well not be there.

 

Yes I guess so, I was assuming it was correctly set up.

[ditchcrawler]

37 minutes ago, Iain_S said:

Any time I've bought an accumulator, it's been charged to a pretty high pressure. I think the last one was at 80p.s.i.

 

 

And that's as bad as being depresurised

[David Mack]

48 minutes ago, Onewheeler said:

If the accumulator is pumped up higher than the pump outlet pressure it won't do anything and might as well not be there.

Which could cause the symptoms the OP is reporting.

[Colecraft Sunflower]

On 29/09/2024 at 11:09, Tony Brooks said:

Unless the accumulator has lost all its pressure I doubt that will be the cause. If it has then a wtaer hammer like episode upon turning a tap off could well cause  those symptoms. A 4 bar PRV should give plenty of headroom for a 3 or 3.5 bar pump to avoid than. Hence I suspect it is pump pressure,

Tony hi - I tested the accumulator pressure and it was zero. And for the first time the system has developed water hammer. Looks like that’s the problem.

On 29/09/2024 at 08:42, David Mack said:

Have you checked the accumulator pressure?

Thank you guys - zero pressure in the accumulator!

[Tony Brooks]

7 minutes ago, Colecraft Sunflower said:

Tony hi - I tested the accumulator pressure and it was zero. And for the first time the system has developed water hammer. Looks like that’s the problem.

Thank you guys - zero pressure in the accumulator!

 

 

Thank you for your feedback & pleased it seems to be fixed.

 

Unless the Schrader valve on the accumulator was/is leaking, then there is a chance that the diaphragm is punctured. If it is, then expect the problem to resurface very soon.

 

 

[hider]

I think that you will still have a problem until you reduce the cut out pressure of the pump.

Tracy had the best way of re-pressurising accumulators without gauges. Sadly missed.

[Tony Brooks]

1 hour ago, hider said:

I think that you will still have a problem until you reduce the cut out pressure of the pump.

Tracy had the best way of re-pressurising accumulators without gauges. Sadly missed.

 

I agree. A 4 bar (say 60psi) PRV and a supposed pump cut out pressure of 1.7 bar (say 27psi) give a pressure difference of over 30 psi, so one hell of a water hammer to jump he valve off its seat. I think there is every chance the pressure is a lot higher than the OP thinks.

[nb Innisfree]

Pound to a pinch of the brown stuff it's 

hydraulic locking caused by a lack of an air cushion between the NRV & PRV, either fit one beween those two (can't remember what they're called!) or remove the NRV. 

[jonesthenuke]

Is the accumulator connected to the calorifier or to the cold supply pipe? If it's on the cold supply it will not anything to protect the calorifier against high pressure cycles caused by the normal temperature cycles of the calorifier. 

 

We have an accumulator on the outlet of the water pump to reduce pump cycling, but there is not one of the accumulator. The accumulator is thus not protected from over pressure by the accumulator when the water inside is heated and the water expands, its just protected by the PRV, as the accumulator is the wrong size of the non return valve on the inlet to the calorifier. As far as I can tell the PRV does not lift (no dribble marks down below the hull outlet). I have thought about fitting an accumulator to the calorifier, but have not bothered. It's a horizontal unit so should have an internal air bubble which will do the same function as an accumulator.  The boat was built circa 2006 and its been ok so far.....