Suction line pressure problems

[Ashwin123]

Hello everyone,

I am quite new to posting, so if I make any mistake or wrongly put information, let me know.

I have been working on a unit lately for a for freezing a tank at -3C for alcohol. The unit uses R22 and these are the pressure I have.

Condensing temp: +42C
Sub-cooling: 5K
Evaporating temp: -15C
Evaporator superheat: 8.5K

The unit has a KVL (crankcase pressure regulator) and a DAS (burn out drier) on the suction line. When I was checking up the the pressures near the port of the equaliser of the expansion valve it read 2.2bar but at the suction valve port it read 1.3bar. Is it normal to have that kind of pressure drop on the suction line?

Another thing I notice is at the expansion valve outlet the tube has frost, is that normal?

[Sandro Baptista]

Evaporating temperature is measure at evaporator outlet or at compressor suction inlet?

-15ºC correspond to 1,96 bar(r).

About the pressure loss, on the KVL is have read 1,3 bar at inlet or at outlet of the KVL?

[Ashwin123]

Evaporating temperature was measured at the evaporator outlet which read 2.2bars.

The pressure was taken at the KVL outlet is 1.3 bar.

[Sandro Baptista]

Evaporating temperature was measured at the evaporator outlet which read 2.2bars.

The pressure was taken at the KVL outlet is 1.3 bar.

Certainly the KVL is making you losing about 0,9 bar, if the suction pipeline and others having no pressure drop, which is impossible. If the suction is too long, many curves, or have a big DP/meter it will contribute a lot to the pressure drop.

[Ashwin123]

The burn out drier also has a has a pressure drop along the line, if I am not mistaken, but yes it is in fact a long line with many risings (existing installation). However when I was opening the KVL, the high pressure dropped and closing it made the pressure rise back but there was no change in pressure on the suction line.

That I think is answered but how about the frost on the outlet of the expansion valve, is it normal?

[Grizzly]

The burn out drier also has a has a pressure drop along the line, if I am not mistaken, but yes it is in fact a long line with many risings (existing installation). However when I was opening the KVL, the high pressure dropped and closing it made the pressure rise back but there was no change in pressure on the suction line.

That I think is answered but how about the frost on the outlet of the expansion valve, is it normal?

Hi Ashwin
You mention a burn out drier.
Is that a suction line burn out drier?
If so how long has it been installed?
Cheers Grizzly

[Ashwin123]

Hello Grizzly,

Yes it is a suction line burn out drier and has been installed in September. Now that you mentioned that I just checked on the Danfoss website and realised that they do those burn outs up to 1-1/8!!! The suction line is supposed to be 1-3/8".

I think I just uncovered the mystery. The guy used the 1-1/8" piping and used it up to the drier and from there he probably increased the pipe sizing to 1-3/8 as the KVL35 is 1-3/8". I couldn't determine that on site as the line was insulated. This is why I had such a big drop in pressure.

[D.D.KORANNE]

Check pressure drop across suction filter ; it could be high due to partial block up

[Ashwin123]

Hi all,

I did have a check today, it seems what the contractors did was using an undersized suction line drier. The suction line is 1-3/8" and is about 16m from the unit, with rising 2 x 1.5m and the suction line drier used is 1-1/8".

This could be the restriction, I believe.

[chemi-cool]

Throw away the suction drier core, it meant to be there only for a short time, a week will do.

[Ashwin123]

I intend to do that. Thanks.