Machined Component Services of Charlotte




How often should I test/service my boiler safety valves?

The following schedules are suggested by National Board Inspection Code (NB-23):
Power Boilers and Hot Water Boilers Less Than 400 PSIG:
Manual check every two months. Pressure test annually.

Power Boilers and Hot Water Boilers Over 400 PSIG:
As determined by operating experience after examination of test history.

Water Heaters:
Manually check every 2 months. Replace valves which do not pass inspection. The cost is low, and since most users do not pre-treat the water, mineral deposits often accumulate rapidly.

Heat Transfer Fluid Boilers/Reboilers:
Must be serviced annually (Per PVG12.2 ASME Section I Code)

How often should I test or service my process safety valves?

Steam Annually
Air & Dry Gases Every 3 Years
Propane Every 5 Years
Refrigerants Every 5 Years
All Others Per Inspection History

Why should I inspect the Valves? Doesn't the State Inspector check them?

In some states, the State Labor Board does inspections. Your insurance carrier or internal risk management team may also inspect your boilers and other vessels. The ultimate responsibility for the safety of your plant and personnel rests with YOU. If you check a valve and it does not work, leaks, or is otherwise not responding like a new valve, you need to replace or repair it immediately.

Which is more economical on-site or shop repair?

It depends on the type of work, the distance from the valve repair shop, the number and size of valves to be tested, and the replacement cost of new valves. Our goal at Machined Component Services is to maximize the service you receive for the dollars you spend. Lift-assist testing of safety relief valves is accepted by most states and insurance carriers.

What is the "VR" program? Is it different from "Green Tag" authorization?

In most states, safety valves must be repaired by a "VR" holder. The "VR" license is issued by the National Board of Boiler and Pressure Vessel Inspectors (NBBI) and insures that safety valve repair shops conform to high standards of workmanship and that all valves which carry a "VR" stamp operate within the tolerances set by the NBBI and the ASME.

The "Green Tag" designation is one issued by Dresser Industries (makers of Consolidated brand safety relief valves) to their authorized distributors. It is a trade designation and is not connected with the NBBI

"VR" holders are authorized to work on any manufacturer's valve as long as the holder can verify critical dimensions. So a "VR" holder can repair Consolidated valves without being a "Green Tag" shop..

That safety valve has never popped off. Why should I worry about it?

A safety valve that has been in service, and has not been tested recently, might not "pop off" because it is stuck shut. Usually, valves demand attention by giving a visible or audible warning such as lifting or leaking; valves which are a silent threat to safety are often overlooked. This is a strong argument for regular safety valve inspection.

Is it possible to test my safety valves on-line without upsetting my steam delivery or production processes?

We can perform on-line testing of most valves. Some valves are set too close to operating pressure to accurately test them. If there is a line surge while we are testing, the product may escape at the lift-gear or cap area. This is especially hazardous with heat-transfer fluid, for example. There must be pressure on the line (usually 75% of set pressure) and the valve must be in contact with the pressure source. Valves installed over a rupture disc cannot be tested on-line.

The safety valve near my steam reducing station has suddenly started popping off. What is going on?

The most common cause is failure of the reducing valve, usually the pilot valve, or mis-adjustment of the pilot, leading to excess pressure on the outlet side of the steam reducing station. Sometimes there is a faulty gauge in the area of the reducing station, causing inaccurate adjustment of the pilot spring. We suggest that you replace the gauge and pilot valve and see if that cures the problem. If the safety valve has lifted frequently, the seating surfaces may be damaged.

I repack my own control valves, but the packing does not last. What is going on?

We suggest that you only use original manufacturer's packing, especially when you are replacing V-ring type teflon packing. It is sometimes necessary to tighten the packing while the valve is in service. If the packing is tightened too much, the teflon is compacted and will not "spring back" to fill the packing area. DO NOT use grafoil or rope packing in the place of teflon v-ring packing-it causes excess drag on the stem, and will require more actuator force to open or close the valve.

Another cause of accelerated packing failure is excessive cycling-the valve opens and closes too frequently. This may be caused by over- or under-sizing the valve, or faulty positioner set-up, leading to "hunting". For help in determining the cause, give us a call (800-528-6639).

I repack my own gate valves, but the packing does not last. What is going on?

Check the quality and suggested uses of the packing in your inventory. Do not use packing specified as "pump packing" for valves, unless this use is approved by the manufacturer. If the shaft and packing gland areas are steam-cut, no packing job will cure this defect. Weigh the cost of replacing the valve against a professional repair by Machined Component Services.

I have a question, but it is not on this FAQ list. How can I get an answer?

Fax your question 704-394-4075 or email it to If you need service, call 800-528-6639.



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