Fooled by TEV

[LRAC]

Not sure whether any of you have experienced this problem before.

Workshop engineer pressure testing a frigo Bohn LUC835C evaporator. After fitting the externally equalised TEV he raised the pressure to 20 bar and carried out a drop test. The charging stub was brazed to the liquid line on the evap and the suction sealed.

When testing he noticed the pressures dropping and proceeded to leak test with bubble solution, Not a sign of a leak but pressure still dropped.
2 engineers assigned to pressure testing thinking we had a duff evaporator. As the job was being installed today i was called to pop down and have a look before we condemned it, i was at a complete loss and decided too leave the unit pressured over night.

This morning the pressure had dropped to 5 bar but decided to try one last thing, i let out the OFN vacked and recharged too 20 bar, no sign of a leak and still dropping.

Decided to put a flame on the coil to see if it distorted the flame or get a hissing noise from a bad joint, nothing.

By accident i inadvertantly warmed the TEV phial and woooosh the valve opened and the pressures in the evap equalised perfectly and held pressure.

We have never been fooled by this before and was wondering what you guys reckon, it was not a MOP valve.:confused:

Regards
Lrac

[Andy]

Hi LRAC:)
yep seen it before on danfoss valve on a freezer:)
ended up pressure testing on both sides of the valve as even heating the TEV didn't work:(

I think it is a differential pressure thing.

Kind Regards Andy:)

[Pooh]

I have seen this sort of thing before but I put it down to the valve shutting due to unsufficiant pressure difference across it, taking that Danfoss TEV's require a delta P of 5bar to open properly I thought that as the pressure in the evaporator came upto a point were I lost sufficiant differential the valve had shut but still leaked slightly. I have since always fitted a shraeder on the suction line and pressure tested from both ends since and the shraeder gives you access for setting up the superheat when you are commissioning.

Ian

[monkey spanners]

Hi LRAC
ive had this happen with danfoss valves when trying to blow out an evaporator due to it being full of water.
All the expansion valve is trying to do is make the pressure in the evaporator match the temperature at the phial, after all it does know the difference between OFN and refrigerant. I warmed the phial with water to get more pressure into the evaporator (OFN into liquid line connection) before opening a large ball valve in the suction to blow all the water out.
(system had so much water in it when i took the suction valve of the compressor, Maneurop, all the oil came out as it was floating on water:eek: I took over his job from another engineer after he had fitted a new compressor, and said it only needs charging as he had to go out that night:rolleyes: )

Cheers Jon

[Pooh]

Monkey spanners I think we have all worked with engineers like that, it comes with the territory.

Ian

[LRAC]

Thanks for the replies guys i thought 3 of us were going mental. It was a danfoss valve so thanks for proving i am not quite insane.

Regards
Lrac:) :) :) :)