Master Catalog>>General Information>>Page Q-8
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Inspection, Testing and Replacement
All relief valves should regularly be inspected to check for contamination and corrosion. If any debris in the valve cannot be totally removed or there is evidence of contamination, the valve must be replaced. Always wear eye protection when examining relief valves under pressure. Never look directly into a relief valve under pressure. NFPA Pamphlet 58, Appendix D, recommends that relief valves on containers of more that 2000 gallons water capacity be tested at approximately 10 year intervals.
Small relief valves used on small DOT cylinders and small ASME tanks should be inspected each time the container is filled and be replaced at least every 10 years. The compact design, high pressure settings, and aging of the synthetic rubber seat discs could result in erratic operation of the valve after a number of years.
Protective Caps
All relief valves must be continuously protected by proper fitting protective caps. Ice, mud, debris and contamination can prevent the valve from opening or, if the valve opens, can prevent the valve from resealing properly. NFPA Pamphlet 58 requires the continuous use of protective caps.
Flow Rate Restriction
Flow rates in the charts are for bare relief valves. The addition of deflectors, pipe-away adapters and piping will restrict the flow. To properly protect any container, the total system flow must be sufficient to relieve pressure at the pressure setting of the relief valve in accordance with the codes.
Short adapters and deflectors designed by RegO® for use with specific valves will restrict the flow only 2 to 5%. Use only RegO adapters on RegO valves.
Adapters with sharp 90° turns will reduce flow dramatically. These should never be used because they can cause the relief valves to chatter and eventually destroy themselves. Long pipeaways with several changes of direction can reduce flow substantially. For more information consult Teeco.
Excess Flow Valves
w Valves
Periodical Inspections for Excess Flow Valves
Excess flow valves should be tested and proven at the time of installation and at periodic intervals not to exceed one year. CAUTION: Testing an excess flow valve in the summer when tank pressures are high will not prove that the same valve will also function under low pressure conditions in the winter. Once a year testing should be conducted during the winter. The tests should include a simulated break in the line by the quick opening of a shut-off valve at the farthest point in the piping the excess flow valve is intended to protect. If the excess flow valve closes under these conditions, it is reasonable to assume that it will close in the event of accidental breakage (clean break) of the piping at any point closer to the excess flow valve.
National LP-Gas Association Safety Bulletin Number 113-78 States: “In order to test an excess flow valve in a piping system, the flow through the valve must be made to exceed the valve’s closing rating. This testing should only be attempted by trained personnel familiar with the process. If no one at the facility has experience in proper testing, outside expert help should be obtained. The exact procedure used may vary with the installation, advisability of gas discharge and availability of equipment. ”In general, most testing makes use of the fact that excess flow valves are ‘surge sensitive’ and will close quicker under sudden, flow surge than under steady flow. A sufficient surge can often be created by using a quick open/close valve to control sudden, momentary flow into a tank or piping section containing very low pressure. An audible click from the excess flow valve (and corresponding stoppage of flow) indicates its closure.
“A test involving venting gas to the atmosphere is hazardous and may be impractical or illegal."
“Any test of any excess flow valve will not prove that the valve will close in an emergency situation. This test will only check the valve’s condition and the flow rate sizing for those test conditions.”
An Explanation and Warning
An excess flow valve is a spring-loaded check valve which will close only when the flow of fluid through the valve generates sufficient force, or differential pressure, to overcome the power of the spring holding it open. Each valve has a closing rating in gallons per minute and CFH/air.
The selection of a proper closing rating is critical. It requires a technical understanding of the flow characteristics of the piping system, including restrictions of the piping and other valves and fittings downstream of the excess flow valve.
System designers and operating people must understand why an excess flow valve, which remains open in normal operations, may fail to close when an accident occurs. Warning: A downstream break in piping or hoses may not result in sufficient flow to close the valve.
Proper Installation
Since excess flow valves depend on flow in order to close, the line downstream of the excess flow valve should be large enough not to excessively restrict the flow. If he piping is too small, unusually long, or restricted by too many elbows, tees and other fittings, consideration should be given to the use of larger size pipe fittings.
An excess flow valve in a pump suction line cannot be expected to close in the case of a clean break in the line beyond the pump, as the pump constitutes too great a restriction, even if running.
Good piping practice dictates the selection of an excess flow valve with a rated closing flow of approximately 50 percent greater than the anticipated normal flow. This is important because valves which have a rated closing flow very close to the normal flow may chatter or slug closed when surges in the line occur during normal operation, or due to the rapid opening
Master Catalog>>General Information>>Page Q-8
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