Wiredraw damage in TXV

Hey there

So this is something that I found interesting. This is a picture of a metering plug out of a Sporlan/Parker TXV on a Frick compressor LIOC circuit. I believe the package that this came off of is about 15 years old.

The reason for the r&r is foaming oil and poor oil temperature control. Disassembly showed reason for the misbehaving valve. Included is a picture of what the metering plugs looks like new.

When I first pulled the valve apart I thought that the erosion was so bad that the metering cone was completely gone, but the new part showed that it wasn’t that dramatic :)

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Hi.
wire drawing of a seat would be totally foreign to most people on this Forum, But is does happen at minimal flow rates unfortunately.
magoo.

Hi Vsimkus
Wire drawing can also occur where there is gas in the liquid line, undercharged system. I have seen some TX valve needle and seats so bad that the valve would hardly open at all because there was so much liquid getting through due to the wire drawing.
This can also happen on pilot solenoids and pressure diaphragm seats over a long period.
Regards
Paul

Danfoss have made massive improvements over the years with wire drawing, using ceramic seats or similar.
ammonia Tx or TEAT seats still need checking, but solenoid pilots & some main seats never see any damage from wire drawing anymore.

http://www.refrigerationcomponents.c...Sporlan717.pdf

Wiredrawing or sometimes called hysteresis occurs when there is flashgas in the liquid line that enters both solenoid valves and expansion valves. This is why manufacturers like to see a few degrees k of liquid sub cooling ahead of the expansion valve to limit possible wear to the tev's orifice and cone and to any solenoid pilot orifices.
This wiredrawing is prevalent in Ammonia systems and ammonia control valves often need replacement internals due to this wear. Over the last few years Danfoss on their ammonia valves have used many different materials to prevent this wire drawing to the nozzles and orifices . They introduced Titanium coating to the pilot nozzles , then tried ceramic but neither of these materials solved the problem.
On the AKVA valves and some EVRA valves the pilot orifices and main orifices would simply be eaten away by the expanding ammonia which when it's moisture level is to high becomes extremely aggressive. The latest material used is called PEK plastic which can withstand this aggressive ammonia erosion and also HFC flash gas
This PEK is used in many ammonia valves where wear to pilot cones and orifices can cause valves to leak bye. So by using harder materials the problem got worse by using a softer material the problem was solved. Valves like the TEAT still have steel parts and still suffer the problem but the AKVA can offer a better solution these days.
To prevent wire drawing keep the system fully charged with clean dry quality refrigerant at all times if in doubt fit a quality drier to the system

Sporlan employed a "flash tube" for years to shift the "worst case" expansion away from moving and seating parts to a "fixed orifice" downstream. Of course these are control valves and at reduced load, the pressure difference shifts back: from the fixed orifice to the upstream point of throttling, that is the metering plug/seat arrrangement. The combination effectively means that the capable turndown for the overall assembly was reduced, or put another way, the valve's stable operating envelope was smaller. Both orifice diameter and flash tube ID's were changed to create different flow capacities from the same valve body....

Interestingly: on the highest capacity valves, their primary approach was to remove the flash tube.

Quote:

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Originally Posted by Glenn Moore

On the AKVA valves and some EVRA valves the pilot orifices and main orifices would simply be eaten away by the expanding ammonia which when it's moisture level is to high becomes extremely aggressive.

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Glenn:
Could you explain why moisture would cause wire drawing in an NH3 system? In a way that those of us who are challenged in the chemical field could understand?

our plant doesn't even have expansion valves, just solenoid and isolation valves, you should see what the seats look like when they finally pull them out.