Originally Posted by
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 .