Pilot operated txv/danfoss pht

[stan1488]

http://www.danfoss.com/IPP/Webforms/...0new%20element hope that link works , can any of you gents please elaborate on the pilot operated function of these valves for me , given that majority of pilot operated valves apply a positive pressure in direction of flow onto diaghram , is that the same ? or am I right in thinking positive pressure is achieved on inlet liquid pressure and flow enabled when pilot line opened , as in a type of vent or relief line , these are the txvs you will see used as a liquid line solenoid as well stan

[Brian_UK]

Sorry Stan, that link isn't working.

[stan1488]

http://www.danfoss.com/products/categories/group/ra/thermostatic-expansion-valves/thermostatic-expansion-valves-exchangeable-orifice/pht/0c79a379-7572-48fe-9cfd-e62a160b2e5d.html

[stan1488]

http://www.danfoss.com/IPP/Webforms/ProductPresentation/Graphics.aspx?ImageCatalogKey=RA-6918e87b-9274-4b1a-a6ca-fdd9ce36df68:RA-56abc46d-9f31-4d0a-911d-a2338abba4c6:RA-0c79a379-7572-48fe-9cfd-e62a160b2e5d:RA-ddbe6b49-5346-4f0f-b675-36960a5a58d5&defaultImage=RA-074ad7af-cced-4754-8818-81050751ac72:RA-56abc46d-9f31-4d0a-911d-a2338abba4c6:RA-0c79a379-7572-48fe-9cfd-e62a160b2e5d:RA-ddbe6b49-5346-4f0f-b675-36960a5a58d5&name=PHT%20new%20element

[Magoo]

Hi Stan

Looks like a PMFL adapted with thermo attached.
When the thermostic pilot opens the pressure on top of the servo piston area vents to suction and vav opens, there is a small balance hole that makes up liquid slowly, the vent line has a greater flow rate, so pressure on piston drops and vav opens by pressure of liquid under the servo piston.
You can fit a solenoid in vent line, that will keep vav shut in off cycle. The external equalizer is fitted to the thermstatic head. You could also fit a gauge in vent line to monitor the vav regulating.
magoo

[stan1488]

thanks for reply magoo , so I was correct in theory , driving force is liquid pressure , quite tricky really , reverse flow compared to a normal pilot operated valve , is it possible to describe the locations in the drawing of servo piston and orifice and flow to pilot line you describe from the drawing? regards stan

[Magoo]

Hi Stan.
The servo piston is attached to the large blue control plug in the flow orifice, the small balance hole is in the piston, the HP liquid is in yellow, the suction side is light tan colour, the external equalizer is in light grey. The vent line goes off the right hand side in yellow as well. The orifice is conical as is the regulating stem so as to get a regulated flow. As opposed to a standard on off cycle solenoid. When set up you get a soft action regulated flow to evaporator. Which, if you have a gauge fitted on vent line you can watch what is going on.
The stem of the thermostatic assembly on top does the liquid by pass to the vent port. Pressure /temp rises the pin stem comes down and opens bypass to vent line.

[Magoo]

Hi Stan.
go to Danfoss web site and down load there industrial and commercial manuals. They will give a very good description of application and operation. Send me a PM and I will send to you if any problems.
magoo

[stan1488]

thanks very much magoo, very clear now ,quite tricky design, most people I know would think it as a standard type pilot applied on top, Im a little pleased thatI was on right track w my theory , all the best keep it cool stan