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After a number of years of service on my solar heater, the frost valve started to leak. This was only a dribble at first by became greater. I tried various methods to correct the problem and eventually discovered the way that it worked and present the fix here.
The NOK valve looks like this on the exterior. It
has threads at both ends.
The right hand end is of a reddish plastic that is screwed into the Black
plastic body.
There is a pin fixing the two together, located in a small hole in the body.
When this is removed the reddish end can be unscrewed with care, as there are
some strong springs inside.
Once disassembled there will be 2 springs, a metal piece and two black plastic parts. One of these is a spider that the metal piece goes into, the other is the actual valve that sits against the rubber seal in the end of the reddish piece.
The spring A pushes the brass body toward the plastic spyder which is limited
by the reddish plastic end piece. The plastic valve body sits on the pin in the
temperature sensitive brass body and the spring B pushes it away from the rubber
seat.
When correctly assembled and at room temperature the pin is forcing the valve
onto the rubber seal and no water will flow out, as the Spring A is stronger
than spring B.
When the temperature lowers to near 6 degrees centigrade the length of the brass
body reduces, spring A pushes the brass body onto the plastic spyder where it
limits, the pin shrinks more and spring B pushes the valve off the seal and
water flows out. The lower the temperature the greater the flow.
Over time the rubber seal gets deformed and spring A is allowed to push the body to its limit on the spyder, This means that the pin will allow the valve to open at a higher temperature.
The fix is to insert a small piece of metal into the hole in the valve so the pin does not go as far into it. Less than 1 mm is required. Too much will prevent the valve opening at low temperatures. In my case a 0.7mm ball bearing was sufficient to restore correct operation.
If you find this of use please send me an email or sign my Guest Book on the main page.
