Piping

[A.Mortezania]

Dear Friends,

At photo below, Sporlan says when system has capacity control and if at this system capacity could decrease below 33%, Proper piping must be same as photo.

I just can not understand why we must connect equalizer line of these two expansion valves together ?

Sincerely yours.
15109

[Glenn Moore]

There is no need to connect the equaliser line as in the drawing , they can be run independently if you prefer to do it that way. There is nothing wrong in connecting the equaliser as per the drawing as it's purely a signal pressure line with no actual flow, and from a practical and a cost point of view it's simpler and cheaper . This line should be either 1/4" or 6 mm, but not in capillary tubing due to potential of blockage with oil or dirt preventing the expansion valves correct operation.
The important pipe arrangement is the 2 suction lines entering the main suction pipe to prevent the top evaporator back feeding liquid into the lower evaporator causing its expansion valve to close and cause the lower evaporator performance to suffer.

[RANGER1]

There is no need to connect the equaliser line as in the drawing , they can be run independently if you prefer to do it that way. There is nothing wrong in connecting the equaliser as per the drawing as it's purely a signal pressure line with no actual flow, and from a practical and a cost point of view it's simpler and cheaper . This line should be either 1/4" or 6 mm, but not in capillary tubing due to potential of blockage with oil or dirt preventing the expansion valves correct operation.
The important pipe arrangement is the 2 suction lines entering the main suction pipe to prevent the top evaporator back feeding liquid into the lower evaporator causing its expansion valve to close and cause the lower evaporator performance to suffer.

Glenn,
I would have thought equaliser lines should be connected directly after TX bulb as per most manufacturers instructions.
This sketch is a bit misleading & generic.
As you mention top unit could influence bottom units performance with suction line the way it is.
It does not show how long riser is & distance equaliser is from TX valve.

[PaulZ]

Hi Ranger
This is the relevant page out of the Sporlan book that Mortezania refers to.
I am with you about placement of the equalizer line, it may be ok if the
configuration is as in fig 13.
Sorry about the photo scanned copy was too big to upload.
Regards
Paul

15110

[Brian_UK]

The diagram is taken from Sporlan document 10-9 and shows a setup for parallel cooling coils designed to stage 50% up and down in response to compressor staging.

If the TEVs were installed with separate balance lines then they fighting each other during 100% operation.

[Glenn Moore]

Hi Ranger
This is to do with systems with capacity control and Evaporators at different levels where oil traps and inverted traps are used to prevent cross flow between evaporators. If the oil trap fills with oil, the equaliser line if fitted after the bulb would lose its ability to give the correct control pressure to the tev.
In normal expansion valve set ups the equaliser would ideally be placed just after the bulb, but in this case there are other elements of the system layout which could affect the Tevs operation and so a slight variation from the norm is required to allow the Tevs to function correctly.
The Tevs equaliser can be run separately or in a common line as shown ,either way is acceptable and will have no adverse effect on the Tevs operation as the suction pressure is normally very stable .
Failure to take into account the variances in the system design can lead to compressor valve breakages and piston and Con rod smash ups due to liquid slugging etc. Tevs can be forced into liquid slugging and the like simply, by compressors loading steps, as every time a bank of pistons load up the suction pressure drops,this sudden drop in suction pressure is felt by the Tevs diaphragm and the tev is forced to open fully for a few seconds before the tev can react to this sudden drop in pressure via the equalising line. The same happens when it unloads
This is just one of the advantages of electronic expansion valves , compressors with unloading gear , as they load up cylinders, the sudden drop in suction pressure has no effect on the electronic valve orifice position, until its sensors change the info sent to its controller, so no liquid slugging occurs, unlike the tev .

[A.Mortezania]

Hi Ranger
This is to do with systems with capacity control and Evaporators at different levels where oil traps and inverted traps are used to prevent cross flow between evaporators. If the oil trap fills with oil, the equaliser line if fitted after the bulb would lose its ability to give the correct control pressure to the tev.
In normal expansion valve set ups the equaliser would ideally be placed just after the bulb, but in this case there are other elements of the system layout which could affect the Tevs operation and so a slight variation from the norm is required to allow the Tevs to function correctly.
The Tevs equaliser can be run separately or in a common line as shown ,either way is acceptable and will have no adverse effect on the Tevs operation as the suction pressure is normally very stable .
Failure to take into account the variances in the system design can lead to compressor valve breakages and piston and Con rod smash ups due to liquid slugging etc. Tevs can be forced into liquid slugging and the like simply, by compressors loading steps, as every time a bank of pistons load up the suction pressure drops,this sudden drop in suction pressure is felt by the Tevs diaphragm and the tev is forced to open fully for a few seconds before the tev can react to this sudden drop in pressure via the equalising line. The same happens when it unloads
This is just one of the advantages of electronic expansion valves , compressors with unloading gear , as they load up cylinders, the sudden drop in suction pressure has no effect on the electronic valve orifice position, until its sensors change the info sent to its controller, so no liquid slugging occurs, unlike the tev .


Hi Glenn more,

Also I think when we use TEV with MOP, When suction decrease suddenly this specification of TEV (TEV with MOP) prevent slugging in these situations.
And regarding filling traps with oil and causing improper TEV working, it is good idea. Thanks.

Sincerely yours.

[Glenn Moore]

Hi mortezania
An MOP expansion valve will also cause slugging under similar circumstances. Sometimes they can be worse if the bulb doesn't have a ballast charge to slow the reaction from the bulb. Most MOP valves use a ballast charge these days to slow the valves reaction too allow the valve to run at low superheat settings and remain under stable control.
An MOP valve is the same as a normal range valve but has a limited charge in the bulb, to limit the maximum operating pressure that the valve can operate at.
An electronic expansion valve has a more accurate MOP setting and can be adjusted to the compressor motors limitation, whereas with a Tevs MOP there are only a few MOP points that you can choose from