Three (3) MUST DO with Excess Flow Valves (EFV)

These were found as I was doing a design spec for a new NH3 Supply Business. These items are directly from the owner’s manual and were presented to the engineering firm after a “debate” on the reliance on Excess Flow Valve(s). These are about the three best manufacturer’s rules for EFVs I have ever seen! When so many companies are going weaker in their spec’s this company decided to say it like it needs to be said…

(emphasis by me)

PROPER INSTALLATION PROCEDURE
- An excess flow valve permits the flow of liquid or vapor in either direction, however, this flow is controlled in only one direction, (the direction of the arrow stamped on the valve). If the flow in the direction of the arrow exceeds the closing flow rate of the valve, it is designed to automatically close.
- Before installing and operating an excess flow valve, take steps to ensure the removal of pipe scale, welding slag, or other debris that could become lodged between the valve disc and the seat.
- Do NOT reduce pipe diameters on the UPSTREAM OR DOWNSTREAM side of an excess flow valve. An excess flow valve depends on flow in order to close, therefore if the downstream piping is too small, or is unusually long, or restricted by too many elbows, tees, and other fittings, consideration should be given to the use of larger pipe fittings.
  - NOTE: When sizing an excess flow valve, good piping practice and field experience suggest selecting a valve with a RATED CLOSING FLOW OF APPROXIMATELY 50 PERCENT GREATER THAN THE ANTICIPATED NORMAL FLOW OF THE SYSTEM. This is important because valves which have a rated closing flow very close to the normal flow may chatter or even close when surges in the line occur during normal operation, or due to the rapid opening of a control valve.
  - CAUTION: The flow rating of the piping, fittings, pump, valves, and hose in an LP-Gas or NH3system MUST BE GREATER THAN THE FLOW RATING OF THE EXCESS FLOW VALVE. If branch piping or restrictions with a smaller capacity than the total system are incorporated, ADDITIONAL EXCESS FLOW VALVES MUST BE INSTALLED at these points.
PROPER OPERATING PROCEDURE
1. ALL VALVES on the upstream or downstream side of an excess flow valve MUST BE IN THE FULLY OPEN POSITION. Partially opened valves will restrict the flow and not allow the full flow closing rate required to shut the valve in the event of an emergency.
2. Pinched or partially cut hoses or small ruptures in piping or fittings will not allow sufficient discharge of LP-gas or NH3 to close an excess flow valve. It is therefore imperative that all operating personnel be familiar with the location and mode of operation of all ESV (Emergency Shutdown Valves) in the piping system.
3. How an excess flow valve works: When a line or a hose is completely broken, the spring-loaded check disc immediately moves to form a metal to metal seal with the valve body. At this point, most of the LP-gas or NH3 liquid flow will cease. The valve will remain closed until the pressure on both sides of the check disc is equalized via the bypass hole through the check disc. At this time the spring will automatically reopen the valve. When a line is completely severed, pressure cannot equalize and the excess flow valve will remain closed until the line is repaired. The bypass hole in the check disc will allow a small amount of product to discharge, and a cloud of vapor will be seen even though the valve has closed properly. An Excess Flow Valve is not intended to shut off bubble-tight when closed, but only to reduce the flow of vapor to a manageable amount until a shut-off valve or ESV can be safely closed.
TESTING OF EXCESS FLOW VALVES
1. After an excess flow valve is installed, the system ~~should~~ MUST [SAFTENG Edit] be tested for proper operation by simulating a break downstream in the system. Most testing makes use of the fact that excess flow valves are “surge sensitive” and will close quicker under a sudden flow surge than under steady flow. To test the unit, pressure the system and then open a shutoff valve quickly at the farthest point in the piping that the excess flow valve is intended to protect. There should be a sudden decrease in flow, and an audible “click”, indicating that the valve has closed and is working properly. WARNING: Only trained personnel should test excess flow valves. It should be under safe conditions, and with the permission of local authorities, since testing with flammable or toxic gases is hazardous.
2. If after testing, the excess flow valve does not operate properly, a thorough check of all piping, fittings, or hoses should be made to eliminate any restrictions that may have reduced the flow of the valve below its maximum closing flow.
3. It is RECOMMENDED THAT ALL EXCESS FLOW VALVES BE TESTED ANNUALLY OR ON A REGULARLY SCHEDULED BASIS to ensure they are still functional. Whenever possible, excess flow valves should be REMOVED AND VISUALLY INSPECTED FOR CORROSION, SCALE, OR OTHER SIGNS OF PHYSICAL DETERIORATION. The check disc must be able to be depressed against the spring onto the metal to metal seat and then snapback open to ensure it is still in operating condition. CAUTION: Testing of an excess flow valve will not prove that the valve will close in an emergency situation. It will only check the condition of the valve (no obstructions on the seat), and the flow rate sizing for those test conditions. In an emergency situation, system piping may be damaged or broken upstream of the excess flow valve so that the escaping product is not passing through the excess flow valve. Good system piping design dictates that all piping, valves, and fittings be as rigid and well supported as possible to allow the proper operation of the excess flow valve during emergency conditions. Since the exact location or nature of an emergency cannot be predicted, it is recommended that when possible, additional shutoff protection by TriPod Safety Couplings at the bulkhead and ESV valves with remote operating controls be provided in addition to excess flow valves.

Source: http://www.squibbtaylor.com/uploaded/Excess%20Flow%20Valve%20Bulletin.pdf

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