The seal inside a brass compressor valve cannot be replaced. If there is an issue with the internal seal, a new valve will need to be purchased.

All fusible plugs are tested in accordance to UL 207, Section 16.  This specification only applies to the test procedure for temperature rating.  We do know they will withstand the saturated pressure of a refrigerant to within 20°F of the stamped temperature of the plug at which point creeping of the alloy may occur.

Creep is a word used to define the appearance of fusible alloy extrusion as it protrudes out beyond the body.  When the plug is under pressure, the alloy can begin to creep as the temperature approaches the alloy’s plastic range.  The “creeping” will continue under such conditions until a leak develops. 

Hydrostatic pressures up to 10,000 PSIG at ambient temperatures have been maintained in the test lab.  However, it is impractical if not impossible, to determine a “creep point” with variations in shell (body) configurations, temperature, pressure, length of exposure, plastic range of the varying alloys, etc.  The shorter the plastic range of the fusible alloy, the less likely it is to creep.

In summary, the fusible plug is a reliable safety device whose primary purpose is to protect a refrigeration system against explosion or fire.  When installed in accordance with such authority as the ASHRAE Handbook, it will be leak proof during normal operation and discharge without failure within 20°F of the stamped temperature.

To determine which RELIEFMASTER® Change-Over manifold will work with a relief valve, all you need to do is match the inlet thread of the relief valve to the threads of the manifold.

Install the manifold where you would normally install a relief valve. Install two relief valves in the manifold. Back Seat (Counterclockwise stem rotation) until the stem stops and apply the proper torque found in our catalog. This will expose the relief valve, which is farthest away from the cap of the manifold, to the system pressure. This relief valve will protect the system from over pressure until it needs to be replaced. To replace the relief valve, Front seat the stem to the proper torque found in our catalog (clockwise rotation until it stops) and remove the relief valve which is farthest away from the cap of the manifold. Once the new relief valve is installed, Back Seat (Counterclockwise) until the stem stops and apply the proper torque. It is also recommended to replace the other relief valve at this time. This can be done once the stem is back seated and torqued properly.

For NPT threads, we offer the following guideline.
For O ring threads, we offer the following torque specs.

The “E” on the end of the callout (NPTFE) is for “external” or male while the “I” on the end (NPTFI) is for “internal” or female.

NPT is a standard pipe thread. NPTF, which is typically used in refrigeration, is a Dryseal pipe thread. Dryseal means no thread sealant needs to be used with the thread mainly because there is more interference but also because the male and female threads are machined so precise.

NPTF Dryseal threads are machined to a sharp point while NPT threads are truncated. Therefore, it can be very difficult getting a male NPTF thread (with the extra material of a sharp point) to thread into a female NPT. In this situation, there is nowhere for the extra material of the male thread point to go.

On the other hand, you can fit a male NPT thread (truncated thread) into a female NPTF thread (point) but there will be space left between the male and female thread. You will need to use an additional method of sealing the threads for a leak-tight seal using this combination.

Yes, the direction the valves are mounted is irrelevant. It is important to make sure that after the valve is mounted, debris is kept from collecting in the valve.

Since Relief Valves are highly regulated safety devices, we do not repair relief valves or supply components to the customer for repair. If the valve is in need of repair, it must be replaced with a new valve.

There are just too many environmental variables to give a definitive answer to this question. Mueller relief valves are used on numerous makes and models of refrigeration systems of all ages and states of repair, various refrigerants and located anywhere from rooftops in the Midwest or Alaska to Navy ships at sea.

By Code, as a manufacturer of Relief Valves, Mueller Refrigeration is only responsible for designing and providing relief valves to the strict standards outlined by ASME Section VIII Division 1. It is up to the user to consult with ASHRAE 15 and their local code for proper installation and use of a Safety Relief Valve.

CE instruction sheet.

A relief valve is your last line of defense in a run away, overpressure situation caused by something catastrophic such as a fire. The closer the pressure gets to the set point of a relief valve, there is potential for leaks and possible discharge. A relief valve needs to be sized at least 25% higher than the maximum system pressure for this reason.

2 years.

All Relief Valves must be replaced after they pop. When a Relief Valve pops, debris can get trapped in the seal and the spring can either rotate or take what is called a “set” which can potentially relax the spring and lower the set pressure. Because of this, relief valves must be replaced in order to function properly.

We are only able to give you a generic Certification of Conformance at this point. Before you call and request the certification, it will help speed the process if you can provide as much of the following information when you call:
Mueller Customer ID: (If available)
Customer name:
Customer Address:
PO number of order:
Mueller Valve Part Number:
Customer Valve Part Number:
Lot Number:
Quantity:
Valve Set Pressure:
Valve Date Code: (vertical 4 digit number stamped on valve. First two digits are week, last two digits are year)
Date Shipped: (If possible)

To determine which RELIEFMASTER® Change-Over manifold will work with a relief valve, all you need to do is match the inlet thread of the relief valve to the threads of the manifold.

For NPT threads, we offer the following guideline.
For O ring threads, we offer the following torque specs.