Liquid Line Filter Blocked!

[Grizzly]

Many years ago I was first taught that a good way to confirm a partially blocked L/L Filter.
Was to measure the temperature difference across it and advised that a differential below 4/5c was acceptable.
I have since come across recommended temperature differentials for Suction Line filters, Which average 2/3c.
But I have yet to find any written data for L/L Line filters.
Can anyone advise please?
Grizzly

[US Iceman]

Hey Grizzly.

Let's examine what happens. If the liquid is not subcooled, then any pressure loss that occurs will mean the liquid is starting to flash off. This process occurs at a relatively constant temperature. If the pressure loss is significant to measure by temperature you can already be generating a high percentage of flash gas by volume.

On the other hand, if the liquid is subcooled then the pressure loss could occur until you reach the saturation temperature for the pressure of the liquid. In this case also, you might not be able to measure the temperature difference.

In both of the above, the temperature loss could be minor but the pressure loss still be excessive.

My practice was to change them whenever I serviced the equipment (leak repair, etc. where the system had to be opened). Or, after several years unless it was an acid problem.

Not a definitive answer I know but it's the best I have.;)

[frank]

Nice reply US Ice.......

[paul_h]

Best resource is systems that are running without fault. I've never seen them run more than 2C cooler out the drier but I work on tiny, insignificant systems.
The smaller the drier, the less likely there is any temp differential, the larger the drier, the more likely there will be some subcooling, but that depends on the current system subcooling as US Iceman says, and I wouldn't expect more than 4C as you say.
Most blocked driers I've seen have had masive temp drops, some to the point of frost forming.
As US Iceman said, it's a matter of maintenance. If there's an obvious problem with the system and there's a significant temp differential across the drier, or the age of the drier can not be verfied, a good pump down to test the compressor and a drier change, TX valve strainer check, can never go astray.

[US Iceman]

Most blocked driers I've seen have had masive temp drops, some to the point of frost forming.


Or, condensation also. I've seen that to. Without the frost or condensation though... it's darn difficult to find the issue unless you have high quality pressure transducers to measure the differential across a drier.

[PaulZ]

Hi Grizzly
The info on Alco inline driers says they have a 7kpa pressure drop which would probably make 2oC about right I would think. I must admit I have never taken temp readings, just feel the line before and after, if I could detect a temp difference I would change the driers.
I agree with US Iceman and paul h about changing them. When ever we do an annual service to a system with driers we always change the driers.
If we open the system for repairs we would change the driers.
Paul

[Dilip sahasrabu]

we normally change when the differential increases beyond 2 deg.C

[Grizzly]

Seems to be my stock answer lately but, many thanks to all those who responded.
I agree with all who say change when the work being carried out warrants it.
And I agree that it can be difficult to determine whether a change is required.
Hence my question!

In fairness to those of us, that work on the smaller systems.It can be a lot more involved when changing a filter is
necessary.
IE They are invariably brazed in place and have no isolation valve/s in the line.
Give me a filter core drier assembly any day.
Next time I get a well blocked filter I will try and get a photo so that I can post it on the forum!
Cheers Grizzly.