TXVs with MOP

[herdian]

Hi all,
Its beginner starting to find out basics of refrigeration again...
I want to know from the practical side, when do we need to use TXV with MOP??

[nando]

Hello,
you have to use a MOP for protection of the compressor.
MOP -10°C, the valve opens when the suction gas pressure is lower than -10°C.
When you have a freezer, after a defrost, the gas pressure can be to high and can break the compressor.
MOP hold the pressure and open when the pressure is low and safe enough for the compressor.
Used in airco has the same function.
Hope i helped you a little.

[herdian]

Hallo Nando...
What do u mean with "MOP hold the pressure" ?
So the valve is completely closed when the low side pressure is too high? My thought was the valve will be fully open if the evaporator pressure is high

[Cewek ITS]

Hallo Tante Ian, you can find the details explanation of MOP in Handbook of HVAC Shan K Wang.

[DVaider]

Hi, Herdian. Check this linc of Alco Controls http://www.astra.dp.ua/upload/do/alco-controls/en_TI__3524.pdf

[nando]

Hello Herdian,
When the pressure is to high, the valve will open a little bit, that time the evaperator pressure is lower than the MOP point.
When the temp. in the room gets down, the evaperator temp. gets lower, the temp. on the bulb from the valve gets lower, the valve opens more. This untill the evaporator pressure is same the MOP point, than the valve is completly open. Than the valve begins to work like normall.
Valve MOP -10°C: when the temp. on the bulb is 0°C, the valve is a little bit open, from -10°C on the bulb, the valve is 100% open and begins to work normall.

[Peter_1]

Hallo Tante Ian, you can find the details explanation of MOP in Handbook of HVAC Shan K Wang.

I don't have that book Uncle Sewec, so what to do now?

[herdian]

OK thank u Nando and DVaider, now i almost completely understand on how this kind of TXV works.
But i have minimum experience on field...so, after a defrost the evaporator pressure will be high, actually what kind of action does this TXV provides to prevent overload of compressor [how does the evaporator can be lowered on its pressure before the compressor starts to operate again]?

[US Iceman]

See the text on page 7 of the link. Look under "Air Conditioning & Heat Pump Applications".

http://www.sporlan.com/10-9.pdf

Maybe this will provide sufficient information for your questions...;)

[herdian]

:p Thanks US Iceman...read, read and read again...
I wonder when will i have a chance to practice it...i think my chance is small...too much expert which is men...:o