Bet you never saw a user-adjustable CP TEV!!

[havertyp]

An unusual application, this, I have stripped away all the electronics, PCB's, wiring, insulation & panels to get to this, it is an Emerson 047680 constant-pressure TEV and is used on a high-accuracy (to 0.001 deg C!!) oil-bath made by Hart (now part of Fluke) and used a lot in the semiconductor industry to calibrate temperature sensors etc. High stage uses R507 and an Embraco J2212GK3-RV hermetic comp. and low stage uses a Copeland KAJB-010E-CAV-800 semi-hermetic comp, running on R508b. The CP valve is adjustable by the user (note the non-standard threaded rod & knurled knob which replaces the usual adjuster screw & sealing cap on the valve: this knob is accessible by the user and a look-up table printed beside it allows the user to set the evaporator pressure (& thus temperature) to suit the setpoint they need: the idea is to balance the heating & cooling power as close as possible to prevent the heater's PID controller constantly over/undershooting and thus unacceptable temperature instability of the test chamber oil (a special non-conductive perfluorinated fluid). This valve was shot, it was not regulating the evaporator pressure, constantly cycling and thus the temperature stability was poor. Just replaced it with a Sporlan ADRI series valve and new charge and all is well. I dont like the idea of these valves being adjustable by the user though, they really are designed to be adjusted by a refrigeration tech and capped off. I think that is what killed the last valve, since it is being tweaked every day and the mechanics must have suffered, it was impossible to turn the knob in the end and the regulation was shot. Would be interested in your opinions on having this type of valve open to user-adjustment on a daily basis and if there are better solutions.