Fusible Plug Versus Rupture Disk in Transport Air-Cooled HVAC System.

[amcfarlane]

Hello. We have installed 281F (138C) / 300psi (20bar) fusible plugs on rolling stock packaged aircooled units (generally R134a) only to have some field failures over time even though 99% max conditions are 172F (78C) / 245psi (17bar). Solder seems to fracture enough to allow leakage but not enough to blow any solder out. Considering changing to rupture disks but have heard stories they leak in vibrating rolling stock situations. Would appreciate any advice. Regards, Aaron.

[Magoo]

I dislike both options, as when failed or releived you loose the lot. Consider using re-seating safety valves

[amcfarlane]

Cheers. We have found reseating type PRV's suffer from "seat bounce" on the trains hence slowly bleed charge over time. Aaron

[mikeref]

Why is your pressures going that high in New Zealand?
No need for pressure relief valves. Install H.P. cut out switches with timed delay if possible.

[amcfarlane]

Thanks. Problem is occurring overseas (most commonly Australia). We have HP switches as well (auto reset with lock out after 3 faults during any 40 minute period). To comply with AS1210 and ANSI/ASHRAE 15-2007, we need low cost PRV for the receivers. We use full resettable PRV's on ships and other relatively low vibration environments. Where no receivers installed, we use low temp solder on pipework.

[Magoo]

Weren't solder plugs made illegal at the start of the ozone hole thing.

[amcfarlane]

Not to my knowledge

[Magoo]

I have never come acoss a problem with seat bounce as you call it and vibration added into formula. Safety releifs on large recip compressors are a prime example of vibration. Perhaps you need to re-assess cheap options. Transport refrig units with all the banging and clanging of trucks and diesel drive motors still use safety reseatable valves.

[Grizzly]

Hi amcfarlane.
I am with Magoo on this one, also I am slightly confused as fusible plugs are designed as fire/pressure relief.
Not what we all would call as true pressure relief valves.
Basically they should lift is the area they are protecting is engulfed in flames and that area gets hot enough to melt the solder plug. Which is why they are sold with a temperature rating and not a pressure one!
They are not used as extensively as they once were. However I to have seen these fail, but only on aged equipment normally.
Where the central button has risen from it's original seat circumference. Usually the rise from it's seat is easily seen or felt.
Most of the above is for general education of others who may not be as knowledgeable as you. I appreciate I may well be teaching you to suck eggs, please excuse me in that!

Yours does seem a strange one and you may well have an issue with the quality of your plugs?

Is this on old or new?

In the EU. solder plugs are no longer allowed to be used with certain refrigerants. So when retrofitting the engineer should consider whether fusible plugs are fitted!
Grizzly
PS r134a may well be one of the unsuitable refrigerants?
I will check! Which may explain the high temp plugs you need?

It's possible the operating range is to high for fusible plugs? Maybe you can advise on that one?

[amcfarlane]

Thank you Magoo & Grizzly. Appreciate your feedback. My personal preference is spring loaded type as well. Opted for rupture disks and fusible plugs originally to save cost, customer specified and because they are legal (at least according to ASHRAE std 15). If cannot find low cost low leakage reseating type, will look into alt suppliers of rupture and fusible type. Aaron

[amcfarlane]

Oops, forgot to answer Grizzly's other specific questions. Fusible plug failures installed to units in service between 2-24months. Plug locations all on high side (receivers). Looking into 450psi rated fusible plugs (just below receiver DP. Aaron

[cadwaladr]

fusible plugs are temperature not psi although i guess they have a bursting point thermo king and carrier use spring type and have for a long time

[amcfarlane]

Cheers cadwaladr. Yes, fusible plugs have a burst rating although they dont legally have to stamp them with pressure (only temperature). Rel high cost for high volume runs and experience with slow leaks is main driver to steer away from spring loaded type (we are a rel small volume manufacturer therefore don't have same buying power as Thermo-King and Carrier). I suppose my main question now is has anyone experienced rupture disk failures due to high / consistent vibration environments?
Aaron

[cadwaladr]

I am not sure on this point,but legally something tells me they are outlawed here thats fusible plugs on new stuff,but not had issues with vibration as i said before tk/carrier have used them on reefers.

[FikeGuy]

We have created multiple solutions for high vibration and refridgeration equipment using rupture disc technology that provide very low leak failure rates and very long service life. If you need help with the application let me know or see www.fike.com and the local Fike representative can asist you with your application. Regards, Bob

[clivemtk]

i think something else is going on here take a tk sb3 or carrier vector boncing on front of a trailer never a problem and they are on 404a

[amcfarlane]

Thanks cadwaladr,fikeguy & clivemtk. After more review, we will revert to Henry rupture disks in lieu of customer prefered fusible plugs as we have 800+ circuits in service for 7yrs+ and only two failures with this type. Will also look at Fike RD's and low cost / low leak spring loaded PRV's. Regards, Aaron.