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Plumbing related question


Tring Man

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11 hours ago, Tring Man said:

 

 

Very interested in DandV comment about an adjustment on the pump itself, it is a flow jet (Jabsco) but I have not noticed any adjustment screw to date. Will have a look 

 

Regards 

Alan 

The adjustment screw may be hidden under a cover plate and is also easily mistaken for just another screw holding the pump together.

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Okay. Have checked and accumulator on cold water side of system even though located next to calorifier. Both pipe connection colour (blue) and temperature of pipe confirm. 

 

Initial pressure according to foot pump gauge connected to the accumulator was 35 PSI, as I had left it (little or no loss of pressure) when I replaced PRV a couple of months ago. 

 

When I then run the water (hot or cold) the pressure reading (at accumulator) dropped to about 27 PSI before pump kicked in, when it rose to 30 PSI at which pressure it remained constant. Remember that accumulator over 50 feet from pump (60 foot boat). When I turned off the tap pressure rose back to 35 PSI in a few seconds and pump cut out. 

 

So everything seems to be setup and working as everyone suggested it should be in this thread. Except that every now and again I hear pump pulsing (usually randomly happens repeatedly every 5-10 minutes for a few hours/day or so before just stopping again) and see water (wetness) down side of boat where PRV pipe exists hull suggesting over pressure. No other signs of leeks anywhere. 

 

Will have a look shortly at pump to see if I can find any adjustment as described by DandV. 

 

Regards 

Alan 

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28 minutes ago, Tring Man said:

Okay. Have checked and accumulator on cold water side of system even though located next to calorifier. Both pipe connection colour (blue) and temperature of pipe confirm. 

 

Initial pressure according to foot pump gauge connected to the accumulator was 35 PSI, as I had left it (little or no loss of pressure) when I replaced PRV a couple of months ago. 

 

When I then run the water (hot or cold) the pressure reading (at accumulator) dropped to about 27 PSI before pump kicked in, when it rose to 30 PSI at which pressure it remained constant. Remember that accumulator over 50 feet from pump (60 foot boat). When I turned off the tap pressure rose back to 35 PSI in a few seconds and pump cut out. 

 

So everything seems to be setup and working as everyone suggested it should be in this thread. Except that every now and again I hear pump pulsing (usually randomly happens repeatedly every 5-10 minutes for a few hours/day or so before just stopping again) and see water (wetness) down side of boat where PRV pipe exists hull suggesting over pressure. No other signs of leeks anywhere. 

 

Will have a look shortly at pump to see if I can find any adjustment as described by DandV. 

 

Regards 

Alan 

Try twisting the top of the PRV to deliberately open the valve under pressure, there might be dirt on the sealing surfaces, that the bigger flow could move.

Other than that, replace the  PRV.

 

Bod

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Okay. Have checked out pump. It is a Jabsco (Flow jet) Par Max Plus 4 pressure controlled pump rated at 15 litres per minute. Pressure switch should cut in at 25 PSI (my cheap foot pump gauge read approx 27 so seems in line with spec) and should cut out at 40 PSI (I read 35 on my guage over 50 feet from pump which is over two years old, so again seems in line with spec). 

 

The only potential adjustment screw I can see is dead centre at top of pump/pressure switch housing and is coloured bright red. On the Jabsco website there is no direct mention of any pressure adjustability, however in one document I found a warning "NOT to adjust the preset pressure adjustment screw", so this must be to what DandV is referring. 

 

I am now worried if I do try to adjust just how sensitive it may be and if I can do more damage than good, at the moment everything works even if I get occasional pulsing. I do not want to end up having to replace a £175 pump.!

 

What is the forum's advice? 

 

Regards 

Alan 

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On 29/12/2019 at 14:16, Alan de Enfield said:

Somewhere between the two figure - say about 3.5 bar

You have jumped straight in with wrong advice.

On 30/12/2019 at 12:35, blackrose said:

 

I agree that the cold water accumulator setting is related to the pump's cut in pressure, and I may have got it wrong but I thought it was meant to be set to a few psi below the pump's cut in pressure as I mentioned in post 5 ? 

You are correct.

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On 29/12/2019 at 18:00, Mike the Boilerman said:

 

The pressure setting for the accumulator should be a little lower than the cut-off pressure of the water pump. I'd suggest 20% lower than the measured cutting-off pressure.

 

Wrong advice. Aren’t you supposed to be a plumber!? If you set the pressure above the cut-in pressure, it means the accumulator will be completely empty before the pump cuts in, resulting in a momentary hiccup of water pressure.

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42 minutes ago, Tring Man said:

Okay. Have checked out pump. It is a Jabsco (Flow jet) Par Max Plus 4 pressure controlled pump rated at 15 litres per minute. Pressure switch should cut in at 25 PSI (my cheap foot pump gauge read approx 27 so seems in line with spec) and should cut out at 40 PSI (I read 35 on my guage over 50 feet from pump which is over two years old, so again seems in line with spec). 

 

The only potential adjustment screw I can see is dead centre at top of pump/pressure switch housing and is coloured bright red. On the Jabsco website there is no direct mention of any pressure adjustability, however in one document I found a warning "NOT to adjust the preset pressure adjustment screw", so this must be to what DandV is referring. 

 

I am now worried if I do try to adjust just how sensitive it may be and if I can do more damage than good, at the moment everything works even if I get occasional pulsing. I do not want to end up having to replace a £175 pump.!

 

What is the forum's advice? 

 

Regards 

Alan 

If you do move the adjustment screw either mark mating  scratches on screw head and body first and also count the turns either way you go so you can always return it back exactly to the factory setting.

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Okay, so conflicting advise regarding cold water accumulator pressure. I had set a few months ago between the cut in and cut out at 35 PSI (cut in is rated at 25 PSI and cut out at 40 PSI) as per advice I read at the time on the forum similar to that provided earlier in this thread. 

 

nicknorman is suggesting (if I understand correctly) that I should reduce to below cut in pressure, so perhaps 20 PSI? 

 

The problem as someone with no plumbing experience is knowing who's advice to follow. At least reducing the pressure would be a change, and so far I have not actually made any changes so can be certain problem not yet resolved! 

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40 minutes ago, nicknorman said:

Wrong advice. Aren’t you supposed to be a plumber!? If you set the pressure above the cut-in pressure, it means the accumulator will be completely empty before the pump cuts in, resulting in a momentary hiccup of water pressure.

Domestic house plumbers often don't know much about boat plumbing.  I had a boat moored behind me once and I noticed the couple on it getting grubbier and grubbier, I thought of offering them a bar os soap but didn't, he could get quite aggressive. Anyway I noticed a chap in overalls kept coming and going all week.

And then the Mrs, owner of the boat came humbly to me and asked me to have a look at their fresh water system as water kept pumping out of the side every time they switched the pump on. In I went to find the chap in overalls, a plumber holding his head in his hands in puzzlement. Took 1 minute to suss, it was the punps pressure switch of course, and they had a spare one in a box that the previous owner had left behind, fitted it and that was that. I was given 1/2 of baccy for my trouble. I should have billed them but because they were neighbours didn't.

    They both looked a bit cleaner next day.

Edited by bizzard
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I would be wary of adjusting the pressure switch as your tests show it to be working to spec. Turning up by say 3 turns, and then back down by 3 does not necessarily mean you are back at median. If a 5bar prv is releasing at a 40psi cut off, it must be faulty or your gauges are out of calibration. 5 bar is , as near as dammit, 75 psi, and if your cauliflower is getting up to that pressure, then something is going to blow. Hefty domestic mains pressure cylinders are only run at 4 bar with an expansion vessel to help with excesses produced with heating.

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50 minutes ago, Tring Man said:

Okay, so conflicting advise regarding cold water accumulator pressure. I had set a few months ago between the cut in and cut out at 35 PSI (cut in is rated at 25 PSI and cut out at 40 PSI) as per advice I read at the time on the forum similar to that provided earlier in this thread. 

 

nicknorman is suggesting (if I understand correctly) that I should reduce to below cut in pressure, so perhaps 20 PSI? 

 

The problem as someone with no plumbing experience is knowing who's advice to follow. At least reducing the pressure would be a change, and so far I have not actually made any changes so can be certain problem not yet resolved! 

Yes it is difficult when there is so much misinformation on here. Despite the fact that this topic regularly recurs!

 

Go back to basics and think what the accumulator is doing... it is acting as a storage buffer. When the pump runs, pressure builds and water flows into the accumulator. When the pump stops, if a tap is opened /still open, water flows out of the accumulator propelled by the air pressure, until the pressure drops enough for the pump to cut in again.

 

So the first point is that if the accumulator air pressure is set above the maximum pump pressure, the accumulator will always be empty. It might as well not be there.

 

Secondly when the accumulator is supplying water with the pump off, it will continue to do that either until it is empty or until the pump cuts back in. Better that the pump cuts back in before it is empty, otherwise there will be a momentary collapse in pressure as the last of the water is pushed out of the accumulator and flow suddenly stops, just before the pump starts.

 

Therefore we want the accumulator to be not quite empty when the pump cuts back in again, and this is achieved by having the accumulator pressure set just below pump cut in pressure.

 

Bear in mind that in order to set the accumulator pressure, the pump must be off with taps open. ie you must set the pressure with the accumulator completely empty of water. Having done this, turned the taps off and pump on, the accumulator air pressure will now be identical to the water pressure, which will cycle up and down as the pump cuts in and out. So if you try to adjust the accumulator pressure now, it won’t work as you are not seeing the base air pressure in the accumulator, you are seeing the water pressure.

 

Just to mention a further point which is that the peak pressure seen inside the system will be more than the pump cut-out pressure, because the water has significant mass and hence momentum once it is flowing, and therefore can’t stop dead. If there is no accumulator in the system, or if it is pressurised higher than the pump cut out pressure, this spike in water pressure at pump cut-out can cause the PRV to momentarily open.

Edited by nicknorman
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Thanks nicknorman for a very comprehensive/clear explanation that even I can follow. 

 

As the rated cut in pressure for the pump is 25 PSI I will set the accumulator pressure to 20 PSI and see how I get on over next week or so. 

 

DandV, thanks for identifying the pressure adjustment screw, I will leave as preset for now. 

 

One final question, everyone agrees 5 bar for PRV is too high, for a 40 PSI cut off pump what would be appropriate considering you have to allow for the mass and momentum of the water as well? 

 

Regards 

Alan 

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4 hours ago, Tring Man said:

Okay. Have checked and accumulator on cold water side of system even though located next to calorifier. Both pipe connection colour (blue) and temperature of pipe confirm. 

 

Initial pressure according to foot pump gauge connected to the accumulator was 35 PSI, as I had left it (little or no loss of pressure) when I replaced PRV a couple of months ago. 

 

When I then run the water (hot or cold) the pressure reading (at accumulator) dropped to about 27 PSI before pump kicked in, when it rose to 30 PSI at which pressure it remained constant. Remember that accumulator over 50 feet from pump (60 foot boat). When I turned off the tap pressure rose back to 35 PSI in a few seconds and pump cut out. 

 

So everything seems to be setup and working as everyone suggested it should be in this thread. Except that every now and again I hear pump pulsing (usually randomly happens repeatedly every 5-10 minutes for a few hours/day or so before just stopping again) and see water (wetness) down side of boat where PRV pipe exists hull suggesting over pressure. No other signs of leeks anywhere. 

 

Will have a look shortly at pump to see if I can find any adjustment as described by DandV. 

 

Regards 

Alan 

No its not, . You need to turn the pump off, open the taps, wait until the water flows and then measure the air pressure, If you pumped it to 35 psi there is no way it can drop to 27 psi  when the tap is turned on

 

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2 hours ago, Tring Man said:

Thanks nicknorman for a very comprehensive/clear explanation that even I can follow. 

 

As the rated cut in pressure for the pump is 25 PSI I will set the accumulator pressure to 20 PSI and see how I get on over next week or so. 

 

DandV, thanks for identifying the pressure adjustment screw, I will leave as preset for now. 

 

One final question, everyone agrees 5 bar for PRV is too high, for a 40 PSI cut off pump what would be appropriate considering you have to allow for the mass and momentum of the water as well? 

 

Regards 

Alan 

The PRV is there to protect the calorifier. The relationship between pressure and force is of course force = pressure x area, and so whilst the pressure doesn’t exert much force on the inside of pipes, taps etc, with the large internal area of a Calorifier, a lot of force is generated. Put that with the ever-thinner walls of a calorifier (due to the price of copper) and you can see that a modest over-pressure can rupture a calorifier. And constant cycling of pressure to very close to the ultimate limit will fatigue the copper and eventually cause failure.

 

So the correct rating of the PRV is only determined by the calorifier manufacturer’s specification. 5 bar sounds high to me, I certainly wouldn’t want to go any higher. But perhaps the PRV is letting go at much less than 5 bar? They can suffer from corroded and broken springs which reduces the opening pressure. I think 3.5 bar is more normal, but as I said it depends on the manufacturer’s design.

Edited by nicknorman
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6 hours ago, Tring Man said:

Already opened PRV to let water flow just before replacing it two months ago for that very reason (did not find any dirt as such but did have some limescale). 

Any scale in the new one?

Could the new one be faulty?  Did fitting the new one cure the original fault, for even a short time?

 

Bod

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