Plumbing woes

[denboy]

ok done all the suggestions new exp tank fitted and prv still leaking,,on the plus side the water pumps a bit smoother.

so i am going to get a 5 bar prv and see if that cures it

[chris w]

i am going to get a 5 bar prv and see if that cures it

I really wouldn't - there's a reason why they all seem to be set at 3bar. It'll all end in tears with a possible big bang!!!

 

Chris

[denboy]

tanks stamped tested to 7.5 bar so in theory with in the tanks safety zone me thinks

[ditchcrawler]

ok done all the suggestions new exp tank fitted and prv still leaking,,on the plus side the water pumps a bit smoother.

so i am going to get a 5 bar prv and see if that cures it

Have you actually measured the pump output pressure?

[denboy]

Have you actually measured the pump output pressure?

no although i have regulated the presure down alot by using the ballvalve fitted after the pump i am still thinking ive just got a duff prv

[ditchcrawler]

no although i have regulated the presure down alot by using the ballvalve fitted after the pump i am still thinking ive just got a duff prv

You cant regulate pressure with a ball valve if there is no flow, just like you cant regulate voltage with a resistor with no flow. The system will still pump up to pump cutout pressure unless you have a tap open to bleed it off

[alan_fincher]

Haven't read the whole thread in detail, but it occurs to me that whilst many boat water pumps only produce 30 psi (so about 2 bar), others can be bought that produce 45 psi (about 3 bar). Given the comments often made about the pressure switches on these, it's not hard to imagine that a nominally 45psi pump could be delivering over 3 bar.

 

Equally I don't imagine PRVs are that accurate either, so a nominally 3 bar one might well open a bit below 3 bar.

 

Do you actually know for certain the pressure your pump produces, please ?

[Big COL]

You cant regulate pressure with a ball valve if there is no flow, just like you cant regulate voltage with a resistor with no flow. The system will still pump up to pump cutout pressure unless you have a tap open to bleed it off

 

What is pressure? My understanding of pressure is a balance of volume of flow versus resistance.

IE for a pump delivering the same known volume, through varying sized open pipes the pressure at the end of these pipes will vary.

If this is true how does one define pressure? A variance in flow rate (volume) will be required to pass through differing sized pipes for the pressure to remain the same at the exit in an open ended system.

Therefore the restriction of flow must have a an effect on the pressure.

Yes or no I await the true physicists for a complete answer.

[Keeping Up]

You talk of an open-ended system. Here we are talking about the pressure which is achieved and maintained in the closed system which exists when all the taps have been closed. A restriction to the flow may lengthen the time taken to reach this pressure, but will not affect the pressure which is eventually reached.

[denboy]

You cant regulate pressure with a ball valve if there is no flow, just like you cant regulate voltage with a resistor with no flow. The system will still pump up to pump cutout pressure unless you have a tap open to bleed it off

Doh point taken

[Big COL]

You talk of an open-ended system. Here we are talking about the pressure which is achieved and maintained in the closed system which exists when all the taps have been closed. A restriction to the flow may lengthen the time taken to reach this pressure, but will not affect the pressure which is eventually reached.

 

Hi Allan

 

Absolutely right, but when whatever it is starts to be used it becomes like an open-ended system.

A pressure regulator is only a spring assisted restriction.

Colin

Edited April 25, 2009 by Big COL

[ditchcrawler]

Hi Allan

 

Absolutely right, but when whatever it is starts to be used it becomes like an open-ended system.

A pressure regulator is only a spring assisted restriction.

Colin

 

He hasn't got a pressure regulator only a part closed ball valve (manually adjustable orifice)

 

But the maximum pressure will be the point at which the pump switches off with no water being drawn off. If the system has no leaks this is how it is for maybe 70% of the time. This is the pressure that the RV is seeing and maybe lifting with. Pump cutoff pressure say 2.9 bar RV lift pressure say 2.8 bar then when the pump cuts out if no water is being drawn off then the RV will lift

[nb Innisfree]

Morn all having a problem with a brand new prv constantly dripping it only stops when i turn the water pressure down to a trickle and leaks even more when the water heats up suggestions please in fact when turning tap on and off it becomes a jet wash

An expansion vessel is called such if it is fitted between NRV and PRV, if it is fitted before NRV it is called an accumulator, same construction different application. If no expansion vessel between NRT and PRV then slightest increase in pressure (due to water in calorifier heating and therefore expanding) will result in PRV opening due to hydraulic locking. An expansion vessel will, as its title suggests, absorb this expansion.

[denboy]

An expansion vessel is called such if it is fitted between NRV and PRV, if it is fitted before NRV it is called an accumulator, same construction different application. If no expansion vessel between NRT and PRV then slightest increase in pressure (due to water in calorifier heating and therefore expanding) will result in PRV opening due to hydraulic locking. An expansion vessel will, as its title suggests, absorb this expansion.

I dont have a none return valve and the exp tank is fitted in the hot water outlet next to clarifier still leaks

[alan_fincher]

Denis,

 

You have not commented on my post 32.

 

Do you know the design pressure of your pump please ?

 

If it were 45 psi (readily available) rather than 30 psi (more normal), I can see that small differences in tolerance of the pump switch or the PRV could easily cause the PRV to leak.

 

If it did prove to be a 45 psi pump, I'd fit a 4 bar PRV, which will give you the necessary margin for it not to leak, but still open well before any potential damage to calorifier.

[denboy]

Denis,

 

You have not commented on my post 32.

 

Do you know the design pressure of your pump please ?

 

If it were 45 psi (readily available) rather than 30 psi (more normal), I can see that small differences in tolerance of the pump switch or the PRV could easily cause the PRV to leak.

 

If it did prove to be a 45 psi pump, I'd fit a 4 bar PRV, which will give you the necessary margin for it not to leak, but still open well before any potential damage to calorifier.

 

Flo king 30 psi

[chris w]

If it's suddenly started blowing the PRV then check the pump's actual pressure. IIRC the FloKing pump has no means of adjusting its output cut-off pressure unlike say Shurflo pumps. A friend of mine had the same problem recently (PRV blowing continuously) with a similar pump and Cleghorn Waring (the pump's supplier) told him that the pump's internal pressure switch occasionally failed and went to a higher pressure. That would explain the PRV trouble.

 

I recently fitted a new Shurflo pump on my water system and although it stated 30psi on the box, it was actually 38psi which would have blown the PRV once the hot water expanded despite having an expansion vessel (maths available!!). On the Shurflo pump there is an adjustable pressure screw on the front face to bring it down to 30psi.

 

Chris

[alan_fincher]

Flo king 30 psi

(No need for such strong language!)

 

Well that at least rules out that the pump is meant to be delivering as much as 3 bar by design, but as Chris says, it may be doing so because of a fault.

[smileypete]

no although i have regulated the presure down alot by using the ballvalve fitted after the pump i am still thinking ive just got a duff prv

 

Errr, that might help explain....:

 

Morn all having a problem with a brand new prv constantly dripping it only stops when i turn the water pressure down to a trickle and leaks even more when the water heats up suggestions please in fact when turning tap on and off it becomes a jet wash

[denboy]

Ok folks thanks so far

just replaced the prv with another one(3bar) still leaking but not as bad.

now the instructions for the pump on the webby site says there is a pressure switch on the front of the pump adjustable via a screw only thing is it isn`t clear whether you screw it in or out to adjust pressure thoughts please

Doh forget that its marked on the pump but its made no difference

Edited April 26, 2009 by denboy

[nb Innisfree]

Ok folks thanks so far

just replaced the prv with another one(3bar) still leaking but not as bad.

now the instructions for the pump on the webby site says there is a pressure switch on the front of the pump adjustable via a screw only thing is it isn`t clear whether you screw it in or out to adjust pressure thoughts please

Doh forget that its marked on the pump but its made no difference

Seems to me that you might have hydraulic lock between PRV and water supply. Only thing I can think of is accumulator not cushioning this, maybe accumulator is pumped up too much?

[ditchcrawler]

Seems to me that you might have hydraulic lock between PRV and water supply. Only thing I can think of is accumulator not cushioning this, maybe accumulator is pumped up too much?

Or a pump putting out 3.1 bar

[chris w]

now the instructions for the pump on the webby site says there is a pressure switch on the front of the pump adjustable via a screw only thing is it isn`t clear whether you screw it in or out to adjust pressure thoughts please

 

You unscrew it to reduce pressure. You can check the actual pump pressure by measuring the pressure inside the water pump's accumulator after the pump has switched itself off. Use a car tyre gauge thingy.

 

Chris

[denboy]

You unscrew it to reduce pressure. You can check the actual pump pressure by measuring the pressure inside the water pump's accumulator after the pump has switched itself off. Use a car tyre gauge thingy.

 

Chris

Ah right good thought thnx going to try another pump in morning 3 weeks to fit a clarifier who would have thought it doh

[smileypete]

Doh forget that its marked on the pump but its made no difference

Unscrew it ALL the way, THEN open a tap to let the accumulator depressurise.

 

cheers,

Pete.

Edited April 27, 2009 by smileypete