Suction check valves SAB 202 / S80

[RANGER1]

Have been working on above machines recently & have observed bleed holes
drilled in suction check valves.
In the SAB202 its approx 2-3mm.
In S80 its approx 8mm (thats big).

I don't see the point of why its done especially on plant running in deep vacuum?

Is it to give easier starting &/or keeping oil sep oil less diluted?

I welded them up!

[Sandro Baptista]

Have been working on above machines recently & have observed bleed holes
drilled in suction check valves.
In the SAB202 its approx 2-3mm.
In S80 its approx 8mm (thats big).

I don't see the point of why its done especially on plant running in deep vacuum?

Is it to give easier starting &/or keeping oil sep oil less diluted?

I welded them up!

When the compressor stops, the non-return valve shuts off immediately and hereby prevents the compressor from running backwards.
The holes should slowly equalise the pressure in compressor and oil separator to suction pressure at compressor standstill.
This should give an easier starting as you said. About the oil if the the internal system is depressurized less amount of liquid refrigerant is allowed on the oil...once again you're right...I mean I agree with you.

[RANGER1]

When the compressor stops, the non-return valve shuts off immediately and hereby prevents the compressor from running backwards.
The holes should slowly equalise the pressure in compressor and oil separator to suction pressure at compressor standstill.
This should give an easier starting as you said. About the oil if the the internal system is depressurized less amount of liquid refrigerant is allowed on the oil...once again you're right...I mean I agree with you.



Sandro thanks for reply

Do you see any danger in welding up equalizing hole?

[Magoo]

Hi Ranger.
I agree, I would weld the holes as well, cannot see the logic of depressurizing the compressor and separator to vacuum suction side, oil pressure pick up at start would potentially risk compressor.
Only thought would be the compressor was not initially selected for vacuum suction conditions.
Stal mini screws years ago had a service by-pass vav around the suction check that a lot of techs left open, not good. The comp back peddled real fast, and slow oil diff at start, regular oil diff faults

[Sandro Baptista]

Hi Ranger.
oil pressure pick up at start would potentially risk compressor.


Don't understand oil pressure pick up...sorry.

About the equalizing this one is done very slowly...the holes are very small and the compressor never would spin backwards. This is a help to start unloading and the oil will not get so much refrigerant on it. The units work well as they are designed don't they. The SAB202 has pre-lubrication pump.

[RANGER1]

The 202 is OK but have had issues with the S80 screws sucking in air when off.
With the 8 mm hole (which I don't know is standard or not but they are there)
pressure equalizes very quickly to suction which is -30 kpa. I think this rapid equalization
is detrimental to seal reliability.
Maybe someone who knows Sabroe's can advise if it is normal to have hole this big & why,
as to me if you do have a hole ,pressure should take 10-15 mins to equalize

[josef]

3. Non-return valve
The non-return valve is mounted on the
intermediate flange pos. 253 and positioned
in the suction chamber. While the
compressor is idle the non-return valve is
closed by means of spring pos. 261. See
sectional drawing.
After start-up of the compressor the
non-return valve opens and the compressor
is able to suck in refrigerant gas.
When the compressor stops, the non-return
valve shuts off immediately and hereby
prevents the compressor from running
backwards.
In valve cone pos. 259 a hole of dia. 6 mm
has been bored which slowly equalises the
pressure in compressor and oil separator to
suction pressure at compressor standstill.

[Josip]

Hi, RANGER1 :)


Have been working on above machines recently & have observed bleed holes
drilled in suction check valves.
In the SAB202 its approx 2-3mm.
In S80 its approx 8mm (thats big).

I don't see the point of why its done especially on plant running in deep vacuum?

Is it to give easier starting &/or keeping oil sep oil less diluted?

I welded them up!


Running compressor with suction pressure in deep vacuum doesn't mean that you do not have any pressure ... on the discharge side due to parallel work of other machines within the same system .... discharge pressure can be up to 5 bar and if your check valve is leaking (usually does after a while ;)) then you start to collect gasses (coming from intermediate vessel) thus condense after check valve and remain in a liquid form within oil separator ... in this case, if your compressor for some reason is standstill for a longer time it can be flooded .... with bleed holes this cannot happen, because all the gases entering into unit are sucked back into LP vessel, this is valid also for diluted ammonia within compressor oil ...

.... bleed holes must match unit size (S81,83,85,87 or 89 -I do not know original sizes) because after 600 seconds your unit can restart automatically and pressures should equalize earlier .. i.e. less then 600 seconds ... in the beginning equalizing is very fast due to high pressure diff, but coming slow as pressures coming close...



The 202 is OK but have had issues with the S80 screws sucking in air when off.
With the 8 mm hole (which I don't know is standard or not but they are there)
pressure equalizes very quickly to suction which is -30 kpa. I think this rapid equalization
is detrimental to seal reliability.
Maybe someone who knows Sabroe's can advise if it is normal to have hole this big & why,
as to me if you do have a hole ,pressure should take 10-15 mins to equalize


sucking air when off :confused:... in this case when compressor is running there must be a lot of oil dripping from damaged shaft seal ... Q: are you sure that you have a leak on compressor itself? .... can be on a lot of places within system running in deep vacuum...

Both machines are equipped with oil pump and oil diff pressure is build up very fast, there is also an oil level switch to stop compressor in case of low oil level..

I disagree with welding of bleed holes on suction check valve .... it is OEM delivery and I'll let them there..... maybe to drill again smaller bleed holes 3 and 5 mm ;)

Best regards, Josip :)