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View Full Version : It's the parts from a solenoid valve! But not as we know it!







Grizzly
25-08-2017, 05:02 PM
Hi Guys Check the attached!

14954

From a malfunctioning EVRA 15 solenoid valve, on a hot gas line.
The coil was humming like a Good Un!
Having replaced the internals the cooler now defrosts!
I have rebuilt a good few EVRA's over the years. but have not had one seized together like this before!
Cheers Grizzly

monkey spanners
25-08-2017, 07:34 PM
Never seen one do that. Had one on a old fosters freezer (one where the condenser is at the bottom with the compressor above, then the evaporator section above that, where the assembly fits in place of a wall panel) where due to the dirty condenser the head pressure had got so high it had squashed the ptfe seat in the solenoid and it no longer sealed. Took the condenser off and washed it in a sink new solenoid and lived to see another day!

Glenn Moore
25-08-2017, 11:19 PM
Hi grizz
This is not an EVRA it's an EVRAT 15 valve. The armature is connected to the diaphragm with a spring. When the coil energises it pulls the armature up and the spring then assists the diaphragm to lift and keeps the diaphragm up and the valve open with little or no actual flow through it. So the EVRAT valves are designed for situations where very little flow is available to keep the diaphragm in a fully lifted state.
The EVRA valve needs a full gas flow through the valve to keep it open , if the flow reduces to much then the diaphragm can start to flop opening and closing and hence damaging the diaphragm causing the diaphragm to stretch and lose its ability to deflect naturally when opening and closing.
The EVRAT valve is great for use in thermosyphon systems where the gas flows are low and in oil return lines where the flow is somewhat variable.
So the EVRA valve is a pure servo solenoid valve which needs a full flow to keep it open and needs 2 psi pressure drop across it to stay open
Whereas the EVRAT valve needs 0 psi to keep it fully open.
Not sure why your using an EVRAT in a defrost line an EVRA is more suitable for that use in hot gas lines the pd's across the valve is always high, sounds like suspect design error or there is something else in the system that demands its use.
Hope that all makes sense, Glenn

RANGER1
26-08-2017, 12:09 AM
Interesting, as Danfoss Australia we cannot get EVRA anymore, only EVRAT because it then has less stock to keep, or rationalize.
Prior to that they were normally used for things like oil return from flooded evaporator where no pressure drop was required.
Not really sure about this picture, spring in armature is missing?
We have to use them for everything for years & no apparent problems except on one occasion would not open when upstream of a Fisher modulating valve.
Years ago seat insert in diaphragm used to "work itself out" not allowing any clearance for armature lift.

Glenn Moore
26-08-2017, 12:18 AM
Hi Grizz
Forgot to mention, when using the EVRAT valve you must use at least a 12 watt coil as the standard 10 watt coil is not really powerful enough to lift the armature and diaphragm assembly. I can guess it has a 10watt coil fitted this will make its function unpredictable when voltage supply and system pressures are suspect

Grizzly
26-08-2017, 05:45 AM
Hit the nail on the head then Guys.
What is shown is what came out, what it was replaced with was what was detailed on the PID schedule.
This particular valve was identified by me as malfunctioning.
Whereas the other 7 are working ok.
All 8 were installed approx. almost 6yrs ago (By fabricating contractors on Our behalf) and I recon this EVRAT got installed by mistake.
The reason its taken so long for any of us to realise there was an issue.
Is because its a 2.0c loading bay chiller and it will benefit from a off cycle defrost as well as the intended Hot Gas timed cycle.

The coils (on all 8 coolers) are all 10Watt so that also leads me to believe that this was a rogue install.
More importantly where onsite might we have a incorrectly assembled EVRAT?
Since replacement I have manually ran the system through several defrost cycles and all is good.
Thanks for the input and info guys.
It has been very helpful.
Virtual rep points to you both.