"" Do Not Memorize what you do - Always know Why you are doing it; understand the basic nuts & bolts of it. So that when it becomes necessary to innovate - you know what can and cannot be tolerated""
Thats a golden nugget of wisdom PHM!!
Question 1 - the power head is the only opening force on the expansion valve . If it fails the valve will slam closed so you will have a low suction and high superheat. If the valve is stuck open then it's probably not your power head it's something in the valve. Of course everything I said is only true if you have eliminated the possibility of there being moisture in the system which can freeze in the valve and cause symptoms of a stuck open or restricted valve.
Question 2- sporlan has published
That one full turn is approx. 4 degrees so 1 quarter turn is 1 degree
Sent from my iPhone using Tapatalk
Question 3 - if you mount vertically because you don't have another option mount it with cap tubes facing up
Sent from my iPhone using Tapatalk
Originally Posted by nchvac
EMERSON CLIMATE TECHNOLOGIES
TECHNICAL HELP GUIDE 2013
To compensate for an excessive pressure drop through an evaporator, the TXV must be externally equalized. The equalizer line should be connected to the suction line at the evaporator outlet, past the remote bulb location so that the true evaporator outlet pressure is exerted beneath the TXV diaphragm.
If I remember correctly, 1/4 turn = 1 degree.
"Real men don’t use instructions, son; besides, this is just the manufacturer’s opinion on how to put this together." -Tim Taylor
JUST A LITTLE CLOSER AND THE LITTER BOX IS ALL MINE!
A couple of thoughts:
There is no magic number of turns per degree of superheat that works for all valves. For example, there are nearly twice the number of turns from fully open to fully closed in a G valve as compared to a balanced ported valve. In addition, there are a lot of factors that could change the amount of superheat/turn from application...distributor sizing (which affects the amount of available pressure drop across the TEV port...which in turn affects the valve capacity), the liquid temperature, which again affects TEV capacity,....
It's a much better practice to measure the superheat and adjust the valve as needed rather relying on opening/closing the valve a certain amount of turns to hopefully get a predetermined amount of SH change.
The reason for mounting the bulb on the horizontal is to eliminate it from sering temperature fluctuations seen every time the trap fills enough to burp a volume of oil up the riser.
If you need to install the bulb on the vertical, the capillary should be at the top of the bulb to prevent the charge from leaving the bulb. But...the way the bulbs are constructed, the charge should never drain out of the bulb anyway...when looking at the bulb with the capillary at the bottom, the end of that capillary inside the bulb will extend up beyond the bottom of the bulb about 1/4". There's no way for the charge to completely drain out of the bulb...plus, the charge will want to migrate to the coldest location anyway....which ought to be the bulb. I have heard from many technicians of control issues when the bulb was installed on the vertical with the bulb pointing down...and after reversing the bulb the valve started controlling fine.
Regarding the amount of pressure drop cross the TEV port: The rating condition for the valve is at a 40* Evap temp, 100* liquid temp and 100 lb pressure drop across the valve port. This is where the 100 lb drop comes from. The valve doesn't really care what the pressure drop is (within reason). where you can have problems is when the valve is selected based on a certain pressure drop...say 150 lbs. when you experience less pressure drop, the valve capacity is reduced. At some point, if the pressure drop continues to reduce, the valve capacity will become less than required. That's the only limiting factor in how low the pressure drop can go...it becomes problematic if it causes the valve capacity to become less than what is required to properly refrigerate the evaporator and maintain required SH under varying load conditions.
In addition some field notes, clean bright and tight. These days were working with smaller suction lines in supermarket most important to get good contact/max surface contact and very tight about two o'clock. Something that works well is insulation over the bulb. Less return air influence on the exterior 97% of the bulb during recovery after defrost and high load pull down . There is a patented superheat sensor that changes the ratio of surface area of the bulb. I would also say on the question of vertical mount that the bulb should be as far possible beyond the last pass of the evaporator, so often I see the bulb in the correct vertical orientation but two passes up from the outlet of the evaporator. I go out of my way to provide a horizontal suction line at the exit of the evaporator.
So what is going to happen as we change to electronic expansion valves?
There are temperature sensors, and usually pressure transducer(s) as well. They will maintain their superheat without need for adjustment, unless there is a system problem or sensor issue.
Originally Posted by lytning
If you want to change the superheat, you do it via a computer or controller.
Yes that is what I thought, I think it is coming sooner rather than later for walk ins and probably some reach ins.
Originally Posted by Mike19