Another pressure relief valve question

L

Louise Busby

Well-Known Member
Joined
17 Mar 2004
Messages
151
Visit site
I have a c-warm calorifier with the usual engine heating and immersion circuits. I keep the boat in a marina so I keep the immersion switched on all the time when I am on board. There is a pretty regular dribble from the pressure relief valve overflow into the bilge which sets off the bilge pump at regular intervals. The water pump also pumps regularly (about every 10 minutes) unless I switch off the pressure. There doesn't seem to be any leak in the fresh water system.

I've just discovered that I am supposed to 'test' the PRV by turning it once a month. When I did this there was a good spurt of water out of the overflow pipe and three big clicks from within the valve.

How do I know if my PRV needs replacing and could this be the cause of the overactive water pump?
 
Yes it is most likely the probable cause of your leak as it vents the cylinder contents (hot water) which would be made-up from cold via your pump.

There should be no leakage from the PRV, however its not unusual for them to leak when tested; some scale/debris often gets under the seat of the valve and when the spring closes it allows a small amount of water to pass.

The clicks you hear is a cam which lifts the valve from its seat and then lets it go, allowing the spring to close the valve.

If the leak persists, try operating the valve numerous times, some time this clears the debris and the valve fully closes and is safe to use. Otherwise you will need to replace it. Not expensive but sometimes a pain to get to!

Best of luck! /forums/images/graemlins/cool.gif
 
If you've twiddled the PRV round a few clicks, Louise, and it's still dribbling, chances are that it needs to be replaced.
It might be affected by chalk deposits if you're in a hard water area, but quite honestly if you were going to the effort of removing it to clean it up you might just as well fit a new one while you're about it. Only about 10-12 quid.
I put up with a leaking one for 5 years, replaced it this year and it's very nice to have one that works properly!
 
OK, so assuming I need to change it I go looking for a replacement.

My tank is a CWB29-VT with 2.5bar valve. Seems to be a discontinued model although it was supplied by Cleghorn. No idea when it was fitted. Boat is 1982 but tank could be later? Valve is a Honeywell TP192 (2.5 bar)

What's the significance of this one saying it only fits tanks made after 1991 and would it be ok?
http://www.cleghorn.co.uk/c-warm-heaters...valve-25bar.htm

There was some discussion of thread sizes on an early topic but how can I know without taking it out first?
 
Hi,
The honeywell TP192 is a combined Temperature and pressure relief valve!.
Which will open to drain in the event of an over pressure (2.5bar) or the contents of the cylinder exceeding the preset high limit temperature.
Its possible that either element or the seat has failed. but on the other hand it may be functioning correctly. If as you say you leave your immersion heater on whilst alongside, if the immersion heater thermostat has failed then the storage temp would exceed the setting of the TP192. and vent to drain.
Does this venting occur when heating the cylinder from the engine? if not then it could be the that the immersion is at fault.
Ideally you need to know the temperature contents of the cylinder and the system pressure so that an informed diagnosis can be reached.

Philip
 
So the PRV is probably faulty and best to replace with new.

The water pump will come on if water is being discharged by the PRV but this should stop when the PRV is changed. It should just come on when a tap is opened.

If it still cycles its probably debris stuck under one of the valve seats. They are easy to take apart and clean , just remember how all the bits go back. If you dont have a filter on the inlet to the pump then add one as this prevents debris getting to the pump and then to the PRV etc.
 
If it was a failure of the temp or HTCO controls the cylinder would overheat or pressure would build and the valve would vent in a gush not a constant weep. In this instance it's almost certainly debris on the seat. I would activate it a few more times and if it does not clear then change the valve. /forums/images/graemlins/cool.gif
 
On the basis of unknown age of the installation but later than 1982 , changing both the combined Temp/pressure relief valve and the immersion heater thermostat, would be desirable.
The valve is there to prevent not just over pressure but also over temperature , if the over temp is close to set point they do tend to dribble and they do also go out of calbration.
But taking into account the age, changing the lot is definately the best option.

Philip
 
Well, you've introduced a whole new dimension now!

Where do I find the immersion heater thermostat and how do I know if it's busted? The water does get pretty hot... is the thermostat adjustable?
 
[ QUOTE ]
Well, you've introduced a whole new dimension now!

Where do I find the immersion heater thermostat and how do I know if it's busted? The water does get pretty hot... is the thermostat adjustable?

[/ QUOTE ]

You should find the electrical cabel going into the tank for the heater element. The thermostat is usually located inside the black plastic wirng cover, and is usually adjusted by a small screwdriver slot.

You dont mention if the water you get out of the hot tap is scalding and spitting/steaming? If it isn't, then it is likely that the thermostat is set about right and working.

If you neglected to rotate the PRV for months at a time, and there was a dribble, it would have built up a calcium deposit in the faces.
Being a tightwad cheapskate, I would dissemble it, clean up the faces, gringd them back in with valve paste, and put it back together again. /forums/images/graemlins/ooo.gif
 
The water is pretty hot, but I wouldn't call it scalding or steaming so hopefully the thermostat is ok.

I've had the boat a year and never knew I was supposed to turn the valve, so being a girl - i've ordered a new one /forums/images/graemlins/blush.gif

The Cleghorn Waring helpdesk assure me that the 2.5 bar one will fit, regardless of date of manufacture.
 
Toby, stop confusing the poor little lady. For it to overheat enough for the valve temp element to operate, the control stat would have had to fail, the HTCO would have had to fail and the water would be very hot indeed from the taps all of the time.

Almost certainly this is a leak through the seat of the PRV due to debris ingress when tested. When it is changed, I am certain all will work well! Louise can tell us who was right later......

Mind you, I would still operate the valve a few times to see if the debris clears!

To see if Toby is right just set your hot water temp low, if the water temp from the tap then drops, it indicates the control stat is working!

Anyway - we shall see! All good advice though, the more the merrier...../forums/images/graemlins/cool.gif
 
I agree the advice given to clear any debris from the seat by manual intervention is good advice and may allow the seat to seal.

But the question still remains as to why the valve has started to pass, there are several reasons and all merit investigation. i.e.
Is the pressure pump cutting out at the correct pressure usually 2bar on small pumps.
Does the expansion tank having the correct priming pressure / volume.
Is the electric immersion inbuilt control thermostat correctly set and operating correctly. The set point generally around 65degC. (Its unusual to find a seperate high limit on the smaller cylinders.)
Is the relief valve in calibration on both temperature and pressure. A pressure gauge is a most usful addition and not expensive.
So rather than to confuse the intention was to inform, and encourage the approach that if a saftey device has operated all other contributing reasons should also be considered.

however as you say, after changing it will work well.

Philip
 
I forgot to mention.....

My boat came with no instructions (new boat) to rotate said valve, and I had no experience of such luxuries prior to thaAt the start of the second season, we were moored at Bradwell marina, plugged in and heater switched on, and we went ashore ofr a BBQ.
When I returned, I could hear the tap water pump running, but with no taps on!!!
I checked the taps and they were shut off, so I tried turning them on. Nothing except air!!
Mystified, I turned the tap electrical supply off, and the din stopped. I then lifted the floorboards to see 300 litres of fresh warm water in the bilges.
The valve had popped, stayerd popped, and of course the pump swoitch saw that as a demand, and so set the pump running. It kept going until the tanks were emptied.
I looked at the hidden side of the tank in a locker, and saw a large sticker I couldn't read. I peeled it off gently and read it: Rotate Valve Once A Month.
I stuck it back on the top of the tank where at least it can be read now.
 
Hey Philip, your advice is good and we all give freely so its good for the OP to consider all options.

HTCO's though are not that unusual - all Targa 34's have a small HW Cylinder but have a PRV and both control and HTCO stats?


Picture050.jpg


23022008198.jpg


Anyway our discussion I am sure has helped Louise, so all is good! /forums/images/graemlins/cool.gif
 
Bad luck - I have been an M&E Consultant for over 30 years, have all the quals and have designed and specified many large scale services systems all over Europe.

I know I should know better, but I very rarely touch my PRV.... once a year at best! Of course, I would always advise people to do so regularly /forums/images/graemlins/confused.gif

Blooming things, often don't seal properly once tested, every service engineers nightmare, particularly on boilers! /forums/images/graemlins/frown.gif
 
You must log in or register to reply here.

Other threads that may be of interest

O
“The Dog that Didn’t Bark:” Yanmar. 4L HASTE.
Replies
2
Views
275
oldgit
O

Share this page

Top