TEV capped off

[Peter_1]

What happens to a TEV with an external equaliser when you disconnect the external equaliser and close it completely?

This will let some rethink to the basics of a TEV.

My son had a service call and the previous tech had no TEV with internal equalisation and simply used one with an external and capped off the connection.

Ran (Unithé Hermétique 1/5 HP) on more then 40 bar (580 psi)/R404a (Needle of the manifold maked a full turn and stopped on 4 bar):eek:
Lucky the sight glass didn't exploded.

What do you think happened?
Problem is already solved but this seemed interesting for this forum, especially because one of my wholesalers said you allways can cap off the equaliser if you don't have the proper TEV.
He's seen this many times :eek:

[Renato RR]

When you do not conect equalizer line to pipe you lose one fors which react together with spring and oposite from force created by TEVs bulb.To conclude TEV can work properly and canot feed evaporator or maintain the superheat degre without conection on pipe.

Renato

[Abe]

What happens to a TEV with an external equaliser when you disconnect the external equaliser and close it completely?

This will let some rethink to the basics of a TEV.

My son had a service call and the previous tech had no TEV with internal equalisation and simply used one with an external and capped off the connection.

Ran (Unithé Hermétique 1/5 HP) on more then 40 bar (580 psi)/R404a (Needle of the manifold maked a full turn and stopped on 4 bar):eek:
Lucky the sight glass didn't exploded.

What do you think happened?
Problem is already solved but this seemed interesting for this forum, especially because one of my wholesalers said you allways can cap off the equaliser if you don't have the proper TEV.
He's seen this many times :eek:



This is what happens, the TEV will close........the low back pressure will drop, fall to a point where it may trip on the Low pressure control.

Then the TEV will open up again, and the unit will start up again, it will keep doing this, like a yo yo....

IE; No stability in operation......

[Argus]

Absolutely.


Hunting is a symptom, but the valve will not control because it is unable to compensate for the pressure drop in the evaporator.

The external line must be connected if it has one, alternatively if the coil is a small one and the Pd can be ignored, change the TX for an internally equalised valve.
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[The MG Pony]

any one who says to cap it off needs their head slapped through a steel bridge support, thats like saying you can drive down a steep hill with no breaks!

[US Iceman]

Or, you could use the externally equalized valve and install the equalizing tube to the outlet of the evaporator coil.

This may not take much longer than looking for the seal cap for the external equalizing fitting.;)

[The MG Pony]

thats what I all ways planned to do in such situations, just a simple under standing of a TXV should indicate that it WILL NOT function with the port capped.

[Peter_1]

I think the tech added more and more refrigerant in an attempt to rise the suction pressure without monitoring the HP.

This thing could have been exploded.

I thought on the first sight that the TEV should close completely and that was what I told my son.
I told him on his mobile that he should replace the TEV with an internal one or connect the equalising line. But there was almost no place for this ( remeber , only a 1/5 HP and a very small evaporator installed in a narrow corner.
Replacing was economically seen for me a better option :D

[Peter_1]

Coming back to my original question: we had the case with the valve which completely closed due to a capped off external equlisation.

But, if you look to the forces acting on externally equalised TEV, then we have the bulb pressure above the diapraghm and underneath it the spring pressure and..nothing anymore because it was soldered at atmospheric pressure.

So the bulb pressure is far higher then the spring pressure, so these forces must throttle the TEV open and it remains open with no superheat at all.
Or like Abe said, open very wide and then close very fast afterwards due to the uncontrolled non excisting SH.

Any thoughts why our valve closed completely and remained close?

[Argus]

Any thoughts why our valve closed completely and remained close?





Assuming there's no flow at all and the built-in strainer is not blocked, I would suspect that the phial and bellows has lost pressure.

.
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[Peter_1]

Assuming there's no flow at all and the built-in strainer is not blocked, I would suspect that the phial and bellows has lost pressure.

.

TEV was newly installed some weeks before they called us, strainer not blocked and bellow was still under pressure (checked it with inserting an orifice where you could feel the resistance of the bellow pressure on a Danfoss TEV)
TEch had increased HP to assures some flow, so you're right , it was not completely blocked.

[Peter_1]

Nobody any idea?
BESC5240, what's your idea about this?