TX valve hunting??

[theapprentice]

Could someone please explain properly tx valve hunting. Im currently working on a unit that has a few problems and one major one is short of gas. What is happening suction pressure sits at about 240kpa then pumps down to about 120kpa when i presume the valve closes rises back upto about 240kpa again sits there for about 15 seconds and im thinking the valve is feeding then start to pump back down to 120kpa when the valve closes again and the unit just keeps doing this while it is running. Is this the valve hunting???

[taz24]

Could someone please explain properly tx valve hunting. ???

You need to understand fully how the valve works to understand hunting.
The valve controls from the superheat on the suction line.
If the valve is sized wrong or if the system is SOG then the valve on occassions hunts.
The valve opens because the coil has been starved of refrigerant (causeing the superheat to rise out of the coil). The valve opens full so the coil floods through and the superheat then falls dramaticaly. The valve then shuts down and starves the coil.
The cycle repeats, valve full open then valve full closed.

If the valve is sized too large similar can occure.

Cheers taz.

[wkd]

You might also want to look at valve temperature bulb positioning and contact to the suction line both of these can cause the valve to hunt.

[taz24]

Could someone please explain properly tx valve hunting. ???

I agree with WKD.

What you must always take into account with a system is its history.

Is the system an established one that has been running ok for a period of time?

Is it a new install?

If it is an established system that has just developed a problem, but has been ok up to that point then you need to find out what has changed. Chances are the design is ok and a component or components has failed.

If it is a new install then the chances are there is a design issue, somthing has been installed incorrectly or a component is at fault.
Commisioning does need to be done by a good commisioning engineer to get the full potential out of any system.

taz.

[afak]

Bulb position after suction line U trap some times results similar case .

[markacs]

1.check The Bulb Position And Were The External Equaliser Is Installed.
2.check The You Have The Correct Size And The Correct Oriface And Refrigerant.
3.check The Application To The Charge.(liquid Cross Charge Or Vapour Cross Charge.)
4.check For Bulb Charge Migration To The Power Assembly Head.take Warm Wet Rag And Put It Onto Vavle Head To Get The Charge To Go Back To The Bulb.
5.check Position Of Bulb On The Pipe!!
6.check For Moisture In The System
7 Check Subcooled Liquid-charge Of Gas In The System.

Mark Liebenberg

[cristopher_uy]

Valve hunting accdg. to the page i read is the overfeeding and starving of refrigerant flow to the evaporator.
Caused by incorrect location of the sensing bulb or the expansion valve itself a defective one.
In my experience,we usually conduct replacements or changes of the following;
1.change filters and oil as well to correct amount,
2.open expansion valve and check its condition if springs okey,clean and install back and make sure sensing bulb is positioned to its original position where these unit run normal lately.
3.check for leaks,vacuum the system and recharged,if no leaks found.
*b4 doing the above steps be sure to recover refrigerant accdg. to your area regulation.
4.charged to correct amount and within amperaged limits.
5.if problem exists in my opinion better replace new valve.

thanx