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Is it posssible to flow refrigerant through a tev orifice in the opposite direction. I ask because i was charging vapour into a system on the suction side, as there wasnt a high side point accessible apart from the liquid reciever valve which i couldnt use due to pumping the system down and the valve being shut. I got nothing in the liquid line after the receiver and before the tev. Hence the conclusion their not biflow.
Why is this so?
Consider the fact that TEVs will close when they sense zero superheat. If you are attempting to charge a system with a TEV from the suction side of the system, the TEV will prevent you from doing so as is will close at the equivalent pressure of the sensing bulb temperature.
What about if you want to pressure test the pipework and evaporator? Are we saying that the tev seats 100% shut during off cycle and there is no equalisation of high and low sides. Would i have to physically warm the bulb up to ensure just a 1% opening, surely not.
Surely yes... :)Quote:
surely not
In fact, warming the sensing bulb up may not help much if it happens to be an MOP (maximum operating pressure) type charge. By definition, these types of thermostatic charges close off the TEV above a certain suction pressure.
Low side pressure is a closing force on a TEV. The higher the low side pressure, the more you force the TEV in a closed direction.
So to summarise we conclude that the pressure( low side )exerted on the spring is far greater than the pressure exerted onto the diaphragm and therefore completely closes the valve 100%.
Actually, low side pressure is exerted on the diaphragm directly, via the equalizer connection, or with an internally equalized TEV, thru the equalizer passageway within the valve body. Bulb pressure is exerted on top side of the diaphragm, low side pressure is exerted on the bottom side of the diaphragm. The superheat spring is an additional force exerted on the bottom of the diaphragm, and it is of course fixed once the valve has been set.
If the sum of the low side and superheat spring pressures exceed the bulb pressure, the TEV will close off. If the TEV does not have a bleed port, don't expect to get any flow across it. And even if the TEV does have a bleed port, you will see very little flow across it.
If you want to pressure test or evacuate a system you have to connect your hoses on both sides of all possible restrictions. This includes the compressor, check valves, switching valves, such as a 3-4-way valve, and expansion devices. Even closed service valves:)Quote:
What about if you want to pressure test the pipework and
evaporator? Are we saying that the tev seats 100% shut during
off cycle and there is no equalisation of high and low sides.
Would i have to physically warm the bulb up to ensure just a 1%
opening, surely not.
I seem to be running into evacuation problems with the (MOP-type) TEV mounted in a small R134a liquid chiller I have built. I only have a low side access point, and I suspect that I have air in the condenser since virtually no heat is released in the top part of the condenser.
Given the fact that I only have a low-side access point, how would I evacuate the system properly? Charging the system is less of a problem since I can charge slowly with a running system.
The valve does not seal 100%. ***** will leak through slowly. It does not seal well enough to leak chaeck half the system.
You should be able to recover and evacuate through the low side only. It will be slow though.
When evacuating a system from the low side, the TEV will open up, regardless if it has an MOP-type charge or not. The problem is the TEV, even when wide open, is a very small orifice for refrigerant to flow thru. As superheat says, it will take some time the evacuate a system this way. Standard procedure is to evacuate from both the high and low sides when access valves are available.
I have put refrigerator driers on small reach-ins just to have a high side port.
Take it that its had a good leak test pria to vacing out and so not drawing air into the system giving a high reading on your torr gauge.
Could try fitting a 1/4" shreider valve on the liquid line by drilling and brazing one in removing shreader before brazing with key, this would make your vacume/charging and possibly future service calls quicker. Depends how much time can be justified on the job.
Take it a pressure/leak test has been carried out so not to pull air in the system when on vac giving high torr reading
Could try brazing a 14" shreider valve in the liquid line, removing shreider first. This would speed up vacume/charging & future service calls. Depends ho much time you have.
Well, I agree on that, but the volume inside the piping on the high side is not large. We are talking about a system which is orders of magnitude smaller than what most of you work with from day to day.Quote:
Originally posted by Prof Sporlan
When evacuating a system from the low side, the TEV will open up, regardless if it has an MOP-type charge or not. The problem is the TEV, even when wide open, is a very small orifice for refrigerant to flow thru. As superheat says, it will take some time the evacuate a system this way. Standard procedure is to evacuate from both the high and low sides when access valves are available.
I suppose that leaving a vacuum pump running overnight would be sufficient. It was also sufficient when I used a captube.