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Old 11-04-2016, 12:54   #1
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Relief Valve

I need to replace the relief valve on our Quick Waterheater.

The maximum pressure on the waterheater is 6 bar.

Does this imply that I should buy a 6bar relief valve ?


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Old 11-04-2016, 13:24   #2
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Re: Relief Valve

Have a look at your original relief valve and see if it is tagged with a pressure set point.

If it's unlabelled, It may be worth checking your normal pump operating pressure, and going half way between the two.

There's no benefit in running the tank pressure at its limit, just an increased risk of tank failure. And you don't want the relief valve opening unnecessarily, as they will fail to re-seat after multiple bleed-offs.
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Old 11-04-2016, 13:26   #3
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Re: Relief Valve

Personally I have never seen a 6 bar relief valve. That equals 87 psi. I would oversize by one half bar more than your water system high pressure cut off. My ISOTEMP takes a 3 bar relief valve with a 40 psi water pump cut off.
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Old 11-04-2016, 15:19   #4
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Re: Relief Valve

Thanx for your replies.

The pump has an openflow of 4.5 GPM , the water is 75C when heated and the boiler has a capacity of 23l.

Is it possible to say anything about the best size of the relief with this information




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Old 11-04-2016, 22:25   #5
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Re: Relief Valve

Quote:
Originally Posted by carlager View Post
Thanx for your replies.

The pump has an openflow of 4.5 GPM , the water is 75C when heated and the boiler has a capacity of 23l.

Is it possible to say anything about the best size of the relief with this information




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None of the above helps.

Pressure ratings come in a number of flavours, for example "working pressure" which is the pressure the system is rated for and usually allows for metal fatigue, corrosion, temperature effects, etc. "burst pressure" is the pressure at which the pressure vessel will rupture. Your relief valve should be set for somewhere slightly above "working pressure" and definitely considerably below "burst pressure".

If you cannot find a working pressure rating marked on the appliance try to contact the manufacturer. Due to the danger associated with bursting pressure vessels it is pretty well standard that manufacturers clearly mark or label them appropriately with pressure data.

If you cannot do any of the above and it is a constantly pressurized system you could put a gauge on the system, observe the pressure where the pump cuts out and put in a relief valve set to say 5psi above this pressure.
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Old 11-04-2016, 23:01   #6
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Re: Relief Valve

Quick Nautical Equipment - DOWNLOADS
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Old 12-04-2016, 02:45   #7
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Re: Relief Valve

The pump a jabsco par-max 3 says 40psi on the label.

40 psi equals 2,75Bar.

Is it correct that the relief valve should be at least 3bar ? and would it be better to use 4bar ?


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Old 12-04-2016, 03:34   #8
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Re: Relief Valve

Looks like the original relief valve would have been 6 bar, at least according to the details on this website
Kit Relief Non Return Valve 1 2inch 6.0B R8 P QKOSPKITVALVE
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Old 12-04-2016, 03:44   #9
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Re: Relief Valve

Here are a few requirements from ABYC that may help:

23.8.12.1.1 Maximum pressure relief shall be set at not more than 175% of the working pressure.
23.8.12.1.2 Maximum temperature relief shall be set at not more than 210F (99C).
23.8.13 Water heaters or system must have a means of tempering the water to 125 F (51C) or less (I believe this is related to engine heated units to avoid creating a scalding hazard).
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Old 12-04-2016, 08:28   #10
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Re: Relief Valve

Turns out that the producer recommends a 6bar relief valve.

Leaving the valve open during winter may cause that it starts leaking.

So remember to shut the valve during winter once the boiler has been emptied.


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