PDA

View Full Version : Double-trunk pistons and thermal-electric expansion valves







seanf
10-09-2017, 08:17 PM
Had never heard of double-trunk pistons and wondered if they still get used?

And dont think Ive come across a thermal-electric expansion valve before, where they used much before electronic valves came in use?

Thanks

FaultCode
11-09-2017, 12:13 AM
Thermal electric ... new one on me too, found this.. not too technical but has got a schematic.
http://bit.ly/2eOTPNb

Glenn Moore
11-09-2017, 08:12 AM
The early thermal electric valve was used in some supermarket cabinets from memory I believe it was Sainsbury's who started the fashion. I think it was someone like Flica who made them. They had a bi metal strip which deflected when heated to push the valve open and then closed as the power was removed.They caused all sort of problems by over shooting and jamming open etc not very reliable at all.
Then the AKV valve came on the market a simple pulsed solenoid eev which anyone could make a controller for. They were first introduced some 35 + years ago . I suppose they could be classed as the first electronic valve . I think some of the problems with the valve was that engineers didn't understand how they worked and therefore were not set up correctly . I remember back in the early days of electronics the engineers first comments when doing training was "how do we bypass them ?"
Trunk pistons were used in the big old twin and large mono block compressors which used massive pistons some 12 to 15 inch diameter with a trunk some 18 inches long with centrifs and screws big machines are no longer needed

HVACRsaurus
11-09-2017, 09:52 AM
Hi,

For your double trunk Compressors the following thread has some photos etc;

http://www.refrigeration-engineer.com/forums/showthread.php?46874-how-do-i-calculate-actual-mass-flow-through-a-compressor-without-flowmeters

But like Mr Moore says they are rarely seen now - lots of moving parts, rod seals prone to leakage, expensive to maintain...

RANGER1
11-09-2017, 11:31 AM
I think in certain fields they are still used, but as said not as much due to screw compressors etc.
Have seen them in air & Co2 compressors (oil free air with teflon piston rings).
Also in gas fields & process plants.

seanf
11-09-2017, 10:19 PM
Thank you Brian, Glenn, HVACRsaurus and Ranger.
Anyone know if there was any real benefits to having the suction valves as part of the piston?

RANGER1
12-09-2017, 09:06 PM
Thank you Brian, Glenn, HVACRsaurus and Ranger.
Anyone know if there was any real benefits to having the suction valves as part of the piston?


I think in in some cases it simplifies design for that type of compressor.
As far as efficiency or performance it would not improve it.

seanf
12-09-2017, 09:57 PM
Thanks Ranger.