Temperature and Pressure Valves

[David HK]

I had an interesting morning and found a shop that sold T and P valves.

The item shown to me - based on pipe size requirements - was rated at 99 Degrees C and 1000 Kpa (about 150 psi). I want something around 4 Bar at 99C.

The interesting thing about this item is that it has a 'one-time' use and after it has popped it has to be replaced. I think it must be designed for a boiler and appears unsuitable for my RE solar hot water system that has reached 112 degrees C on several occasions during 2011.

This brings me to the question- What are other people using that would suit my needs where temperature can easily exceed 100 Degrees C?

I have done some Googling and found sites that sell T & P valves with various ratings, but cannot find a technical spec sheet that explains if repetitive use is possible.

Does any Forumite have knowledge of website URL's that may be more revealing on this subject?

David in HK

[Watt]

I'm not sure of a website but, any chance you can search for domestic water heater temperature pop off valves?  As far as the pressure relief, I would think you could get any water pressure relief valve to work that is adjustable, even if you have to put it on the cold inlet side of the heating system.

[Bryan1]

Hi David,
             Years ago I made some brass pressure relief valves out of brass and if you like I can strip one and put up some pic's. They ain't hard to make provided you have a lathe of course... . The ones I made were for air but being brass they would also be suitable for hot water but I would redesign them to have a pipe for the pressure relief rather than hot water spurting everywhere. Basically all you need is a SS ball and spring then a means of adusting the spring for the required pressure.

Regards Bryan

[bj]

   David:  have a little experience from a previous life,  T and P's are designed for one time only on the
temperature side, to force the user to investigate the cause.  The pressure side can be used a few times.
  I believe almost all domestic stuff is this way.
  Bryan's cure would be elegant, but if you don't have a lathe, try commercial air system PSV's.  Some of
the better ones have discharge connections, (not just holes) but the discharge cannot be restricted in
any way or function will be compromised.  This however will not take into account any temperature issues,
but rapid release of pressure at above boiling will quickly cool things down.
  Most are brass, and are suitable for Water/Oil/Gas.
  Hope that isn't just a hindrance.

[Wolvenar]

Ross has rebuilt a pressure relief valve in the past and posted that here. I am not sure if you need the temperature portion.
http://www.anotherpower.com/board/index.php/topic,33.0.html

[David HK]

Thanks for the replies, most interesting.

I shall keep studying the subject for a while and may opt for pressure relief only.

One thought is a solenoid valve linked to a circuit which has a thermistor sensor. Should work in theory but the location of the sensor would be important. Then of course, no voltage and it would cease to function.

David in HK

[Wolvenar]

Yeah, I would ditch that idea.. Stick with a simple mechanical fail safe if it is really a factor.
Mr Murphy's natural prey is complexity.

[RichHagen]

Since most of the domestic ones are set for domestic water, or low pressure boiler tanks, I think that finding one for 4 bar and a suitable temperature for that pressure might be a bit problematic.  If you did have a tank rupture at that pressure with the water just below the boiling point at that pressure I would think it would be quite disasterous with the instant flash to steam, so caution with your system is certainly in order.  Rich

[RichHagen]

If you were to go with pressure only, then you are in the realm of steam boiler relief valves, but I don't think they are generally rated to handle liquid water.  An example from the Google would be:
http://www.boilersupplies.com/safety-valves/safety-valves.html
If it vents at the temp and pressure you describe, you would be venting a mixture of water and steam as a portion of the water would flash to steam once the pressure was reduced upon passing through the valve.

Rich

[David HK]

Thanks for the note Rich.

I am going to stick with a basic pressure relief valve which is already installed but calibrated differently from its original factory setting.

I am therefore making up a calibration jig of pipes, a pressure gauge, a car tyre valve, and a foot pump.

I will put up a photo when its finished.

David in HK