Sporlan EF Series TXV Question

[shellkamp]

Read the last sentence....

Yes but how is it achieving that?

By eliminating (or greatly reducing) the liquid pressure as an opening force.



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[shellkamp]

Huh?

The balanced port valve has a taper on the pin that allows for more precise metering at lower loads, and therefor, can meter the refrigerant efficiently over a wider range of tonages.

The tapered pin might be an additional feature; but the "balanced" in "balanced port TXV" has to do with the liquid pressure as an opening force

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[BBeerme]

Technically, although liquid pressure does affect the amount of refrigerant going through the orifice, it is not an opening force.

The tapered pin might be an additional feature; but the "balanced" in "balanced port TXV" has to do with the liquid pressure as an opening force

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[shellkamp]

Technically, although liquid pressure does affect the amount of refrigerant going through the orifice, it is not an opening force.

Tell sporlan they're selling balanced port valves under false pretenses, then.

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[VTP99]

Yes but how is it achieving that?

By eliminating (or greatly reducing) the liquid pressure as an opening force.



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Correct as stated here....

[shellkamp]

Correct as stated here....

Exactly: so let's put it all together now.

A TXV's function is to control superheat

A balanced port TXV is able to accurately control superheat under a wider range of operating conditions by reducing the liquid pressure as an opening force.

The "varying load" is a misnomer - it should be "varying operating conditions", which would really in-turn translate into "wide range of head pressures" seeing as how the load (of the box) is supposed to remain relatively constant (we'll leave blast chillers and the like out of this conversation).

Wouldn't you agree?

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[VTP99]

Well now, on a small reach-in on the line, you could have a lot of door opening and closing.
But... those are typically cap tubes....
Reach in freezers more likely.

[shellkamp]

Well now, on a small reach-in on the line, you could have a lot of door opening and closing.
But... those are typically cap tubes....
Reach in freezers more likely.

Yes but that isn't what the balanced port is meant to compensate for - a regular TXV adjusts itself just swell to changes in indoor load.

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[BBeerme]

There are other factors. Like multiple stages of unloading, multiple TEV's on a single circuit, and multiple compressors on a single circuit.

For what it is worth, and for those that don't already know this, an expansion valve controls better near it's maximum capacity, and has more problems controlling near its minimum capacity. So if your load determines a valve selection between two valves, choose the smaller valve.

Yes but that isn't what the balanced port is meant to compensate for - a regular TXV adjusts itself just swell to changes in indoor load.

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[VTP99]

Yes but that isn't what the balanced port is meant to compensate for - a regular TXV adjusts itself just swell to changes in indoor load.

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Then Sporlan should edit that last line on
"BALANCED PORT DESIGN"

Unless that's meant to reference widely varying outdoor operating conditions.

[shellkamp]

Then Sporlan should edit that last line on
"BALANCED PORT DESIGN"

Unless that's meant to reference widely varying outdoor operating conditions.

I guess technically that's correct since at it's core the balanced port feature is negating the effect of "pressure drop" across the valve - which would go both ways with the suction and liquid pressure.

But I still stand by my previous statements.

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[BBeerme]

And in the end, we all learn something . . . LOL

[Dchappa21]

Balance port valves are pretty much all we have installed for many many years now, and yes it's because they can be used with low liquid pressure. Thats the main reason to use a balance port for valve for the varying load (ie outdoor ambient). I see a lot of new condensing unit coming through with 150psi headmaster's now for 404a, r448a, and balanced port valves seem to do a great job with less than a 100psi diff across the txv.

[pecmsg]

Trying to eliminate/mitigate the 10-20# swing in suction pressure after the fan condenser fan cycles off and my head pressure starts to build. I wouldn't imagine a system with a headmaster would necessarily need balanced port due to the steady head pressure.

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One problem you may have is the current Ambient temperatures and winds (Beyond Design Conditions).....the headmaster may just not be able to bypass enough refrigerant to maintain pressure and flood the condenser. I've found at or below Zero the headmaster has trouble maintaining especially if windy. Block off 1/2 of the condenser and see if things stabilize...........If not i use ICM325 instead of fan cycle. Less swinging.

[Guyinfield]

Well... didn't intend my post to become a debate about BP valves. If this was an excersise in confidence I failed miserably.

Just to rap it up. I did not add in my initial post that the system was short of gas. I did add refrigerant on the initial service call, but wasnt able to identify a leak. On return I found a leak (possibly several) in a rotting section of the evap. Also confirmed headmaster had failed, but was not stuck as I originally wrote up. Would in fact have had to be cut out of system before going forward. Tacking on the age of the equipment owner opted to replace system.

Basically my concern with the TXV was me weighing my concious vs my company,s will. Not a great spot to be stuck in but only happens every once in a while. Thanks to all who threw in their thoughts and resources.

Pecmsg, I will look into the icm 325. Have seen them on equipment but never stocked or installed.

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[2sac]

Well now, on a small reach-in on the line, you could have a lot of door opening and closing.
But... those are typically cap tubes....
Reach in freezers more likely.

Fractional systems like Federal open air cases all use balanced port because the door is open all the time

[bunny]

In looking at the common force balance in a TEV, there are typically three forces mentioned:

(1) Bulb pressure, which will increase/decrease as the bulb temperature increases/decreases. This pressure acts on the top of the element diaphragm, and is the force that drives the valve open.

(2) Evaporator Pressure, which acts on the bottom of the element diaphragm. This is a closing force.

(3) Adjustment spring pressure, which also acts on the bottom of the diaphragm. This is also a closing force.

The evaporator pressure and spring pressure together comprise the total closing force in the valve force balance.





The standard TEV has an additional opening force...the liquid pressure acting on the surface area of the TEV piston. the force is determined by the liquid pressure (lbs/sq in) multiplied by surface area of the piston (sq in), and acts in the opening direction. Where this opening force starts to become significant is when the TEV is required at low load conditions. As the load reduces, the valve throttles closed to maintain the superheat set-point. Yet, while it's attempting to maintain the superheat set-point with the valve throttling, there's this large force (liquid pressure) trying to open the valve. The result is that the standard TEV has a finite range that allows it to operate in reduced load conditions, and still maintain the superheat set-point. The standard valve can reasonably maintain its superheat set-point to load conditions that are approximately 50% of the TEV capacity. So, a standard TEV with a 1 ton capacity will maintain the superheat set-point to a point where the load is approximately 1/2 ton. If the load reduced below that, the valve will have difficulty maintaining SH.



The balanced ported valves were designed to eliminate the effect of liquid pressure as an opening force. Doing so allows the valve to operate at a lower percentage of its total capacity and still maintain the superheat set-point. This can be critical in preventing floodback, and the resulting compressor damage in VAV air conditioning systems, which might have wild load swings between the dead of summer, and the mild load demands in the spring and fall.

The O valve utilizes a specially designed piston that (1) has a Teflon piston ring which isolates the bottom half of the piston from the top half of the piston, and (2) two passageways which allow the liquid inlet pressure to pressurize the bottom of the piston.

There's no way to prevent the liquid pressure from acting on the surface area of the top of the piston. However; this design allows that same pressure to act on the bottom of the piston...thus eliminating the effect of liquid pressure as an opening force.



The smaller balanced ported valves for refrigeration achieve this "balancing", or eliminating the effect of liquid pressure as an opening force. They utilize a single pushrod, and the valve seat is integral to the pushrod. The area of the seat that is exposed to the liquid inlet pressure is where the "force" acts upon, and will contribute to the valve's opening force. The shoulder that is machined into the upper portion of the pushrod creates a surface area that allows the liquid pressure to act upon, but in an opposing direction, again eliminating the effect of liquid pressure as an opening force.

Balanced ported TEVs can effectively operate down to approximately 25% of their rated capacity, and still maintain their superheat set-point.



These smaller balanced ported valves were created for a different purpose. As supermarkets systems started to be operated at lower condensing pressures in the cooler months to increase efficiency, it became very apparent that the TEV was the limiting factor in determining how low the condensing pressure could be reduced. The problem is that TEV capacity is in part based upon the pressure drop through the TEV port. As the condensing pressure is reduced, it also reduces the pressure drop through the TEV port. At some point, if the condensing pressure is continuing to be reduced, you'll reach a point where the TEV capacity becomes less than the evaporator load...meaning that the TEV then becomes too small.

There were two solutions to this problem: (1) limit how low the condensing pressure could be reduced, or (2) develop a valve that could be oversized in the summer months when the condensing pressure is at its peak, yet still have sufficient capacity during the low condensing pressure operation in the colder ambient temperatures in the winter.

The balanced ported valve achieves the desired result. It can effectively be oversized for operation in the summer months, as it has the ability to operate down to 25% of its rated capacity. And because it is oversized at the design condition, there is sufficient capacity in the lower condensing pressure periods in the winter time.


One misnomer about the balanced ported valves is that they somehow "either largely reduce or eliminate the effect of pressure drop across the valve port".

There are two ways in which pressure drop across the TEV port effect the valve: (1) the liquid pressure as an opening force, which is described above. Indeed, the balanced ported valves eliminate the effect of liquid pressure as an opening force. (2) the greater the pressure drop across the TEV port, the greater the capacity. This is true for a standard TEV and a balanced ported TEV. The fact that a valve is balanced ported does not in any way change the fact that increased or decreased pressure drop (which means increased or decreased mass flow) will result in increased or decreased capacity.

The elimination of liquid pressure as an opening force will result in a more consistent superheat control. But the effect of fan cycling, which results in fluctuations in liquid pressure (meaning fluctuations in the amount of pressure drop across the TEV port), and the resulting fluctuations in TEV capacity, will cause balanced ported valves to be somewhat less consistent in their ability to maintain superheat.

So, Balanced Ported Valves:

They eliminate the liquid pressure as an opening force.

This allows the valve to operate satisfactorily, maintaining its superheat set-point, down to a lower percentage of its rated capacity (approximately 25%).

It also will result in more stable superheat control, since the liquid pressure is no longer able to influence the valve's opening.

[TPARSONS64]

It is not a balanced ported by the number you shared on the valve. That is a standard Sporlan TXV. I thing that is a sweat R22 valve but the last number eludes me....it should be a C for medium temp or all the numbers are not shared. They will have a B or they are rated in capacity by A or double A and do not have a tonnage size on them. Although I prefer balanced ported valves....they are not required if you have a headmaster and/or a fan control. Balanced ported just means there is an extra port in the valve to keep pressure on the diaphragm to keep suction pressure high when head pressure falls.....they work fantastic! If your headmaster is not going to be replaced.....and if it was me.....I would install a balanced ported TXV to keep suction pressure up. Head pressure is very important on R22 systems due to the orifice in the TXV is half the size of R404A and R134A. Otherwise you may have a freeze up due to lower head and suction pressures. I learned that one the hard way.

Tim Parsons

Tim Parsons

[Poodle Head Mikey]

How precise is this highlighted statement ?

PHM
--------

It is not a balanced ported by the number you shared on the valve. That is a standard Sporlan TXV. I thing that is a sweat R22 valve but the last number eludes me....it should be a C for medium temp or all the numbers are not shared. They will have a B or they are rated in capacity by A or double A and do not have a tonnage size on them. Although I prefer balanced ported valves....they are not required if you have a headmaster and/or a fan control. Balanced ported just means there is an extra port in the valve to keep pressure on the diaphragm to keep suction pressure high when head pressure falls.....they work fantastic! If your headmaster is not going to be replaced.....and if it was me.....I would install a balanced ported TXV to keep suction pressure up. Head pressure is very important

ON R22 SYSTEMS DUE TO THE ORIFICE IN THE TXV IS HALF THE SIZE OF R404A AND R134A.

Otherwise you may have a freeze up due to lower head and suction pressures. I learned that one the hard way.

Tim Parsons

Tim Parsons

[TPARSONS64]

Probably not enough.....being precise is not my objective. It is to provide my experience and opinion to help people diagnose troublesome service problems that only can be found be trial and error. If information and this industry would be precise, there would be no call backs and equipment would not break down as much. With that said, I encourage additional comments that are precise, because it would explain a lot. That would help all technicians to understand what is truly going on and have answers and knowledge, instead of having their thumb in their ass and can't find any support.