Hot Gas Bypass

[troymedhurst]

Hi All

Came across a compressed air dryer today that fed hot gas after expansion valve and into suction line before expansion valve sensing bulb.

Outlet from bypass valve went to a tee, then it went through check valve, then connected before evap and after tev. This I am familiar with, but from tee it also went directly into suction line before sensing bulb.

I am aware you can have hot gas in suction line, with a de-superheating txv.

but why both?????

Unit is a ultratroc hpd4200. R134a
2 bar suction. Hot gas bleeding in.
11-8bar discharge. When fans cycling.
Full site glass. Evap outlet constant 1.5degrees
Comp suction return ranging between 3 and 15 degrees
I think this is happening when tev closes ant hot gas is going straight into suction line! Then hot gas warms sensing bulb then opens tev again! Constantly seeing temperature swing at comp inlet?
I cannot see why you need both?


Any help explaining this would be great

Troy

[Magoo]

To maintain a constant even dew point in whole HX for maximum water separation and stop risk of icing up.

[troymedhurst]

Magoo
thanks for the reply
I still do not understand the principal of what you have said, could you explain further.

many thanks troy

[RANGER1]

www.danfoss.com/NR/rdonlyres/A8033C20-B3CA-4105-B3E5-D6B5D653A79A/0/TCHE.pdf


Try this link, probably need exact model of hot gas byass valve.
Sounds a bit strange from your description, but you do need a suction sensing point for the bypass valve.
Does the tee'd off line going to suction line have a stop valve in it? If so maybe close it & see what happens.
Has it worked in the past?

[troymedhurst]

www.danfoss.com/NR/rdonlyres/A8033C20-B3CA-4105-B3E5-D6B5D653A79A/0/TCHE.pdf


Try this link, probably need exact model of hot gas byass valve.
Sounds a bit strange from your description, but you do need a suction sensing point for the bypass valve.
Does the tee'd off line going to suction line have a stop valve in it? If so maybe close it & see what happens.
Has it worked in the past?

Thanks for link Ranger

The bypass valve on the system is a standard type, only has inlet and outlet and 1/4" equalising line. It doesn't have a desuperheating liquid injection line either.
Other that the extra feed into suction line, before Tev sensing bulb, it is a normal standard installation of a hot gas bypass.
I have to remove refrigerant charge on another identical unit, I may install 1/2" isolation valve and monitor system and report back.

Thanks again Troy