NORMALLY OPEN VENT VALVE
MAIN AND BLOCKING VALVES These valves are always normally closed valves. They can be manual reset or motorized, depending on system design. Valves must be approved for this service. All North American 1518/1519 Valves are FM, UL, and CGA approved/listed and meet insurance underwriter requirements for natural gas, propane, and #2 oil.
NFPA 86 does not require the use of normally open vent valves. If your insurance underwriter or jurisdictional authority insists that a normally open vent valve be used on your system, we recommend that you give the valve duly required attention. These valves have occasionally stuck open during operation of the combustion system. If this occurs, large volumes of fuel can vent to atmosphere unnoticed. This could be both extremely costly and potentially unsafe. Leak testing devices are not permitted on the vent line. Therefore, your choice of a more expensive normally open vent valve that contains a "proof-of- closure" switch could be advantageous.
Figure 1. Typical component arrangement showing vent valve.
High and low gas pressure limit switches must be downstream from high gas pressure regulator. Equipment should be arranged in this order:
manual valve, gas strainer or filter, high gas pressure regulator, relief valve (if used), low gas pressure switch, main automatic shutoff valve, A leak test cock, normally open vent valve, high gas pressure switch, blocking valve, B leak test cock, manual valve, and ratio regulator (if used). 11 10
TEST PROCEDURES Reference NFPA 86 for leak test procedure. Insurance underwriters prescribe a modified leak test procedure when a normally open vent valve is used. A licensed electrician can install a simple circuit on existing systems to allow proper leak testing. Procedure should include testing of flame safeguard and all limit monitoring devices. Test cocks with hose nipple adapters are shown as A and B . Also needed are a short length of hose tubing and a clear glass of water. Avoid damage to test cocks. Replace with plugs after testing. CONTACT YOUR LOCAL AUTHORITY HAVING JURISDICTION, OR NORTH AMERICAN, FOR ANY ASSISTANCE THAT MIGHT BE REQUIRED WITH DESIGN AND USE OF CIRCUITRY TO HELP ATTAIN MAXIMUM SAFEGUARD AND APPROVALS FOR YOUR PARTICULAR SYSTEM.
NOTE: IF BUBBLES CONTINUE AFTER ANY RECOMMENDED LEAK TEST, CLOSE MAIN MANUAL SHUTOFF VALVE AND PERFORM CYCLING ROUTINE DESCRIBED UNDER "PRE-START TESTING". RETEST LEAKING VALVE AFTER CYCLING. IF BUBBLES DO NOT STOP, VALVE IS STILL LEAKING. REMOVE LEAKING VALVE FROM SERVICE. This reference also provides an excellent example of preventative maintenance procedures to help you construct and implement your own schedule. North American fully agrees with, and refers you to, the latest edition of NFPA 86 for additional information including the need for frequent testing of the entire combustion and limit safeguard system.
Instructions 1518/1519 Page 6
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