Balanced Port TEV

[lana]

Hi everybody,

I was wondering if anybody used Balanced port TEV?

The manufacturer claims that this kind of TEV can give the same capacity (more or less) when head pressure drops.

The basic working principle is OK but I would like to know how effective this design is.

Any comment would be appreciated.

Cheers
LANA

[yangchenchen]

Balanced port TEv is used widely in refrigeration system. when the refrigeration capacity is high than 8KW , it is advised using Balanced port TEV.
can anyone give more detailed advantages about Balanced port TEV ?
best regards
yangchenchen

[BESC5240]

Hi,

The minimum superheat you need to start to open the valve is the static superheat. (this creates the force just enough to overcome the initial spring force).

In single port TEV the pressure on the inlet of the expansion valve (= condensig pressure = Pc) has an influence on the opening of the valve.
A high Pc helps to open the valve; in this way it reduces the static superheat, S.S..
The influence of the Pc on the static superheat is depending on the construction of the valve (dimensions and geometry of the orifice, cone/ball, ...).
In a fixed condition the capacity of the valve is directly related to the total superheat (including static superheat).
Concluion : If the Pc influences the S.S., it also influence the capacity of the valve.

In balanced port TEV the influence of the PC on the opening of the valve is eliminated by the construction of the valve. In this way the capacity (directly related to the superheat) is not influenced by the change in Pc.

Now, the question could be : why are not all TEV balanced port? Well, it has a certain price tagg.

[wambat]

Balanced port valves are designed for systems that experience fluctuating pressures. On conventional TXV's when the pressure drop across them changes so does the amount of superheat, Potentially you could have either flooding or overheating of the compressor due to this reason. The balanced port cancels this effect allowing proper superheat to be maintained
These have been used for many years and have been effective

[lana]

Hi everybody,

Thanks for the comments.



In balanced port TEV the influence of the PC on the opening of the valve is eliminated by the construction of the valve. In this way the capacity (directly related to the superheat) is not influenced by the change in Pc.



In ASHRAE there is a picture showing the Balanced port valve which I attached here. There is one more pressure (P4) inlet pressure acting on the push rod.
This made me confused:confused:. Either the explanation is not clear or it is meant that the P4 cancles on the push rod because of two equal areas.
Any comment?

Anyway, this is about how they work but how effective this is? I mean if we use this type of TEV do we have to have heat pressure control as well?

Cheers

[BESC5240]

Hi,

In my first post I wrote " the pressure on the inlet of the expansion valve ... has an influence on the opening of the valve " .
This inlet pressure is the same pressure mentioned as P4. I simplified this by calling this pressure 'condensing pressure Pc' , which is most cases is correct (not taking into account any pressure drop in the liquidline).

Now, does this mean you can forget about head pressure control ? NO.

This P4 does not influence the static superheat of a balanced port TEV, but ...
the capacity of a TEV is also related to the pressure drop between inlet and outlet, dp = P4-Po-dPx,
where dPx are all pressure drops to be considered in the plant (mainly caused by the distributor, if present).

So, head pressure control is still important, to secure a minimal P4 and indirectly a dP over the valve.

[lana]

Hi BESC5240,

Thank you for good explanation.

What you mention is exactly my question. If still the head pressure must be kept at a design level to get proper Dp across the valve (to get the capacity), then what is the real advantage of this kind of TEV? As you mentioned before they are more expensive too.

Does Danfoss manufacture this type? Is there any literature on this?

Thanks again.
Cheers

[Samarjit Sen]

Hello Lana,

I am regularly using Balanced Port TEVs in all my projects. I find them very effective and with the drop in pressure, there is no change in performance or capacity. I advice those who come to me for suggestion, to use Balanced Port Valves.

[BESC5240]

Hi Lana,



Does Danfoss manufacture this type? Is there any literature on this?


In the different ranges, several valves are available with balanced port (b.p.) design:

TE5 - T55 range : TE55 are b.p.
TDE range : TDEB are b.p.
TGE range : complete range is b.p.

It's clear that the larger the orifice/cone surface, the bigger the influence of P4 will be, and the greater the need is for b.p. valves.

[lana]

Thanks everybody.

Still I am not satisfied and I have to read more.:cool:

Cheers

[US Iceman]

Hi lana,



If still the head pressure must be kept at a design level to get proper Dp across the valve (to get the capacity), then what is the real advantage of this kind of TEV?


Based on what I have experienced with these valve types the minimum allowable differential pressure is greatly reduced. Therefore, the much lower differential pressure allows the discharge pressure of the system to be drastically lowered, which saves a lot of energy.

And as a result of using a balanced port TXV the superheat control is very reliable even at the low differential pressures.

So...in my opinion the real advantage of using these valves is save energy which might have been used by the compressor(s), while providing stable superheat control.;)



Still I am not satisfied and I have to read more.:cool:


Reading is fun!!:D

[Samarjit Sen]

Maybe this link may explain to some extent.

http://www.emersonclimate.com/flowcontrols/pdf/TXVs%20-%20All%20You%20Need%20To%20Know.pdf

[lana]

Thank you Samarjit Sen and US Iceman,

Dear Samarjit Sen,
I have that article but thanks anyway.

Dear US Iceman,
Thanks for your explanation.

What I understand is this :
In normal TEV inlet pressure (Pc) acts as an opening force but in balanced port Pc is canceled out.
BUT still valve capacity depends on Dp across the TEV. Dp depends on Pc too:confused:.

Low Pc decreases the capacity but it does not increase the super heat. IS this the case?

Sorry guys, either I am confused or I am getting old:p.

Thanks again.
Cheers

[US Iceman]

Sorry guys, either I am confused or I am getting old:p.


Oh, I don't think you have anything to apologize for. I'm older than you and I don't get my knickers in a knot over some of these details.:D

I have not spent a lot of time trying to understand the intricacies of balanced port valves.

The valve capacity is still based on differential pressure, while the forces are balanced out to allow stable superheat control.

The valve has to supply sufficient liquid to achieve the cooling capacity required at the low differential pressure condition. In effect, this becomes a part-load condition the valve must be capable of reacting to, while still meeting the full load condition.

That is the way I look at it, but I'm open for a better description.:o

lana, you must have a lot of topics that keep you awake during the night.:p

[lana]

Hi US Iceman,



lana, you must have a lot of topics that keep you awake during the night.:p


YES indeed.
Yesterday after this discussion I went to jim BUT still I was thinking about this valve:confused:.

Anyway, a very dear friend (who is a member of this forums), took some time and explained to me in detail. Now I understand the whole idea. I thank him sincerely.
I share it with you what I understand.

There are two different items to be considered.
1- Static super heat of the valve.
2- Capacity.

Condensing pressure (Pc) effects both items.
Fluctuation in Pc changes Static super heat in normal TEV. But with balanced port this fluctuation is kept to literally zero.
Still, fluctuation in Pc changes the capacity of the valve whether balanced port or not.

This is the summery of what I understand and it satisfies my curiosity;).

Cheers

[US Iceman]

Hi lana,

I hope you are well.



Condensing pressure (Pc) effects both items.
Fluctuation in Pc changes Static super heat in normal TEV. But with balanced port this fluctuation is kept to literally zero.
Still, fluctuation in Pc changes the capacity of the valve whether balanced port or not.


I think we have an agreement. Since the evaporating pressure is fixed by the application, the Pc (or what I call the liquid feed pressure to the valve inlet) determines the available differential.

Myself, I do not like the term Pc since it implies condensing pressure. What the valve is reacting to is the liquid feed pressure at the inlet of the valve, which forces you to consider the liquid line pressure (and other effects) loss, plus solenoids, filter-driers, service valves, etc.

The balanced port design helps to achieve stable operation (re. stable superheat control) as the Pc changes.

PS. I have things that keep me up at night also.;)

[lana]

Dear US Iceman,

Thanks a lot for the explanation of Pc. I could not agree with you more.

Cheers.

P.S. Don't stay up long.:D you need some rest.

[128cyclist]

One big difference in a balance port valve is the needle/seat in a standard valve the needle and seat are tapered so it takes more pressure difference to get a change. A balanced port valve needle and seat are almost squared off. This allows for very small pressure difference to allow flow change. This is why many people say they don't like balance port valves because they hunt.
One solution to this is to adjust and set the superheat at 105 condensing. One problem that occurs when floating head systems if you set your superheat in the winter or during low head conditions when it get warmer you will experience flood back. When you do this you will see little to no hunt and have very good superheat control down to low head pressures. Note when you start floating head you may need to go to a larger expansion valve then you are use to because of the loss of valve capacity due to the lower pressure difference between High and low pressure. I have had to use a 48000 BTU TXV on a 15000 BTU load for instance. I have used Bohnmiser kits from BOHN for years one thing that they did was put the sensing bulb into a tee into the refrigerant flow which also gives quicker responce. They invented the Balanced port in conjunction with Sporlan.

[US Iceman]

This allows for very small pressure difference to allow flow change. This is why many people say they don't like balance port valves because they hunt.


That is a new one for me. I have not seen any of the balanced port valves I've used do this. In fact, quite the opposite. They have been very stable.

I also don't adjust new expansion valves. The static superheat setting from the factory has given very reliable control and no flooding problems. On a short coupled system you might see this, but the ones I worked on had fairly long lines (supermarket) and that may have minimized any potential floodback, but that's just a guess on my part.

In some instances the pressure ratios at low head have been no higher than 2:1 and the valves have performed remarkably well in my opinion.

[US Iceman]

you need some rest.


And I intend to get some too! It's been a long day.;)