filter drier question

[cleverd]

how do I know if a filter drier is clogged and needs to be replaced? How can I check it?

[Sandro Baptista]

cleverd,

Mount a sightglass downstream the filter. If you have sure that the liquid line is full of liquid (well charged system) then if the filter drier is clogged then bubbles on the sight glass should appear, due to the partial expansion of the liquid (flashed gas). Also if you feel the liquid line, after the filter colder than the inlet it means that is clogged by the same reasons as above.

[Magoo]

Check the inlet versus the outlet temps with contact thermometer.
There are many schools of thought of were to put sight glasses, before drier or after drier. Partial blocking will create a minor pressure drop which will be detectable with thermometer. I use one of those electronic UV thingos

[Aik]

Also you may check pressure drop through the filter with manometer.

[Grizzly]

Also you may check pressure drop through the filter with manometer.

There are not many systems in the U.K with suitable test points to adopt the above!

Magoo has suggested the most obvious and practical solution.

I tend to measure the liquid line temp either side of the filter as suggested.
Observing the TD if it is say 4-5c differential.
Time to change the filter.
4-5c is my rule of thumb, others may do differently.
Most times when the filter is blocked you can feel the difference across the filter.
common symptoms of a blocked filter include,
High suction S/Heat, High Head pressure (or even HP cutouts) or LP / LP cutouts.
On larger systems with a maintenance contract we change them once a year as standard.
Cheers Grizzly
Grizzly

[chemi-cool]

Grizzly, you should not have any temp Δ across the drier if it is OK.

even 1°C difference means its done its job and the system already loosing capacity.

[james10]

"2k it's had it's day" said the old charge hand.
what i think he meant was anymore than 2 kelvin accross the drier it needs changing

[Sandro Baptista]

common symptoms of a blocked filter include,
High suction S/Heat, High Head pressure (or even HP cutouts) or LP / LP cutouts.
On larger systems with a maintenance contract we change them once a year as standard.
Cheers Grizzly
Grizzly

High Head pressure it could happens or not...it depends of liquid receiver so the condenser can always be free of liquid bulk accumulated.

[Sandro Baptista]

...it depends of the liquid receiver storage capacity...

[cleverd]

thnks guys, i tested some today with my pipe clamp and found a bad one

[Grizzly]

even 1°C difference means its done its job and the system already loosing capacity.

Sorry but some of the windswept locations and paint encrusted pipework I encounter.
Makes a 1c diff almost impossible to measure.
Which means that a little latitude is needed.
By all means change the filter when you see fit.
Usually there is quite a difference.

High Head pressure it could happens or not...it depends of liquid receiver so the condenser can always be free of liquid bulk accumulated.

And for systems that don't have receivers?
There are an awful lot of chillers that don't have receivers!
( The condenser acts as one.)

Sorry maybe I should not of used the term common!
Let's be honest a blocked filter should not be a common occurrence if the system in question is being maintained properly?
I should of said could occur.
Don't take me to literally guys, I was posting a general set of comments.
The effect of a blocked filter does depend upon the system involved surely?
Grizzly

[monkey spanners]

One thing to keep in mind is that you might not be the first engineer on site after the drier has started to be restrictive.
Previously someone could have seen bubbles in the sight glass and added refrigerant. This will then back up into the condenser causing the subcooling and head pressure to increase till the sight glass clears, then then dier continues to get progressivly more restrictive...

On one system i was called to on a farm, in fact we just called in as we met the milking parlour fitter on another farm down the road and even he could tell the system wasn't right and asked if we would call in just to see what we thought.
Found the ice bank tank to have had the txv opened up fully, a bigger orifice fitted, and the phial fitted to the liquid line
All because the drier was blocked and they couldn't get enough refrigerant to flow to meet the load.

First thing i do now if i suspect a system is short is check for a temperature difference across the drier.

[Sandro Baptista]

And for systems that don't have receivers?
There are an awful lot of chillers that don't have receivers!
( The condenser acts as one.)

That's why I have said in a previously post "High Head pressure it could happens or not". But don't hurry Grizzly I see your point.

[joe magee]

I hate to be a pain in the rear but isn't it called a liguid line drier and a suction filter.

[the chiller]

if in doubt change driers on both high and low sides