Fusible plugs?

[monkey spanners]

Found a fusible plug today with 10mm of solder sticking out, but not yet leaking. Where do we stand with replacing these as some wholesalers have stopped selling them saying they are illeagal, and advising replacement with a plug. Others are happy to still sell them :confused: Its on a copeland ZR61 scroll unit.

Cheers Jon

[US Iceman]

Hopefully someone from the forum in Great Britan will have a copy of the refrigeration safety code so they can provide a direct answer to your question.

If the fusible plug has some solder sticking out, my guess is it has seen repeated or sustained high temperatures, but not quite high enough to "blow the plug".

In the US fusible plugs are allowed in unitary equipment of some sizes.

If there are no other pressure relief devices on the system, replacing the fusible plug with a blind pipe plug is, or should be illegal. I would seriously question anyone who said this was legal.:eek:

Think about this... If the fusible plug is removed and there are no other pressure relief devices installed, what prevents the system from blowing up (if a blind pipe plug is used)?

[Argus]

As far as I am aware, fusible plugs not banned in the UK but are not permitted on equipment that is greater than Category 1 in the PED. You'd need to check this with the PED guidance notes.

They can be and are used on small systems without liquid receivers where it is impractical to use pressure relief valves.

The main problem in obtaining replacements will be matching the melt temperature.

.

[Brian_UK]

Double up on high pressure safety swiches and plug the hole.

Personal advice only, not law.

[The MG Pony]

I plan on replacing a 6000BTU plants plug with a HP cut out tied to a blow out valve, basicly replicating its function will adding a control to it.

IE: Rather then tie the HP to the condencer tie it to the receiver (Where the plug is) to get the HP cut out messure, and the blow out via a T line so we can put both controls into one clean spot rather then strewen about the system.

[Abe]

Last year I had a receiver with the fusible plug jutting out but not leaking. By July it had pushed out due to high head pressure.

Keep a check on it and take steps now to rectify. By summer will be too late

[Argus]

.

The solder insert in fusible plugs is tapered in the long section so that it does not push out and become a projectile. It is deliberately shaped this way so that it does not respond to pressure.

If the head of the thing is proud of the brass plug it means that the system has overheated at that point at some stage, then cooled down sufficiently for the plug to re-set.

The fusible alloy is temperature calibrated. If it moves, I'd recommend you change it and look for the reason.

.

[monkey spanners]

I think i will try and get some with a higher temperature rating as 73C seems a bit low when the system runs at 65C. Will have to check the maximum pressure for the reciever first.

Cheers Jon

[Peter_1]

72°C and 65°C is far too high for returning liquid out of the condensor

[monkey spanners]

Hi Peter
73c is the fusible plug melt temperature and 65c is the condensing temperature on the first milking on a DX milk tank with an evaporator covered in milk at 20c (could be 35c with no precooling:eek: ) in warm weather.
Have seen the suction gauge in the retard section on the first milking with a copeland ZR40 scroll on a 3000L tank with no precooling.
On condesing units built by the tank manufacturer i belive they set the hp switch at 450psi on R22. Though they also fit bigger condensers.
On farms the condesers soon get blocked up with cow hair, straw, milking vacuum pump oil, cowsh*t dust and if your unlucky cattle cake dust which i'm alergic to:( so they do tend to run hotter than ideal. Also the cows lick the fins flat if they can get at them:confused:
The most important thing is to cool the milk as quick as posible to reduce bacterial growth in the milk as its stored for two days on the farm before picking up by the dairy company. So the compressors tend to get caned a bit.

Cheers Jon

[Peter_1]

Well, I serviced a long time mil coolers from Muller, BijDeLey,DK and Packo.
I can see the Packo factory here out my office while typing this message. http://www.packo.com/en/?from=homepage

I've never seen such a high pressures on compressors.
I told the farmers to switch on their compressors as soon some milk was in the tank, not waiting until it was full.
Another good feature for milk coolers is a heat reclaim boiler, they need anyhow some hot water to spray on and rinse the ...(don't know the name of the 4 nipples coming out at the underside of a cow LOL :p :D (better never answered this message :D ))
As soon the compressor starts, after 5 minutes they have warm water.
We made the boilers ourself in the past and I posted here already some pictures of it.
It's not that difficult.

Packo makes a milk cooler with an integrated ice bank generator system in it to avoid this excessive pressure rise. http://www.packo.com/en/library/12/rmib.pdf

[monkey spanners]

The first Packo tank i fitted i had the agitators running backwards:o I had seen the green sticker on the back of the tank with the arrow and took it to be agitator rotation (it was 11pm and made sense at the time) Turned out to be superheat adjustment instructions( in belgian) The customer still hasn't let me forget it ten years later:D
The ZR40 with the high suction pressure was on install day so the unit was a bit late starting and the farmer had yet to plumb in the platecooler, being done the next day with the new milk delivery pipe to the tank.

Cheers Jon

[Peter_1]

...superheat adjustment instructions( in belgian)

Jon, what's 'in Belgian'? Wasn't it a unit made in Ireland?

[monkey spanners]

Hi Peter
Said something like "kwaliat" with an arrow. Thought it was made in Belgium, so assumed it was Belgian. Maybe its Irish, showing my ignorance now! All the ones ive put in lately have come from Ireland, but this was 10 or 12 years ago. I think at one time they where made in colingbourne Kinston/Ducis in wiltshire in the UK and badged as Hosier. Good tanks apart from the back cover/finger amputator (RMIB)
:D no offence meant:D
Ive mostly fitted Serap tanks, so know more about these.

Cheers Jon