Charles, As strange and contrary as it sounds, a single interlock preaction system with less than 20 heads may not need any air or nitrogen source. So it then wouldn't need the low air switch either.
Is this really correct? 7.3.2.1 describes the 3 types of preaction systems (1) Single interlock (2) Non-interlock (3) Double interlock Then 7.3.2.4 Supervision The annex describes supervision as constant monitoring of pipe and detection equipment to ensure the integrity of the system. It then explains that a single interlock system of more than 20 heads is required to be supervised but not at a minimum pressure. The handbook also describes why a minimum pressure of 7 psi is required on non-interlock and double interlock but doesn't mention single interlock. 7.3.2.4.4 states; All precation system types described in 7.3.2.1 (2) non-interlock & (3) double interlock shall maintain a minimum supervising air or nitrogen pressure of 7 psi. It does not mention Single interlock. If you do decide to install a compressor or nitrogen source, it needs to be an automatic source of air or nitrogen with an AMD. You can't just rely on "Joe the maintenance guy" to turn on the compressor occasionally. What if Joe goes on vacation or gets hit by a bus? Also, you don't have a low air supervisory switch ring a bell. A bell is associated with alarm; fire, get out of the building. Low air is just a supervisory condition, that's when you call Joe the maintenance guy. Then you find out Joe got hit by a bus... Kind regards, mike Mike Henke CET Sprinkler Product Manager ___________________________________________________ Potter Electric Signal Company, LLC 1609 Park 370 Place, St. Louis, MO 63042 phone: 800-325-3936 | direct: 314-595-6740 [email protected] | www.pottersignal.com -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Charles Thurston Sent: Wednesday, December 17, 2014 6:19 AM To: Colin Carew (Cambridge) Subject: Re: single interlock pre-action less than 20 heads Hello Colin, I'm no expert, But reading 7.3.2.4.1 the word "automatically" triggered in my mind that if there is less than 20 heads, You still need the compressor. Just don't need the pressure switch to turn the compressor on/off, Maint guy could go by and cycle it daily or as needed. Would still need the low air switch but it is allowed to just ring a bell on the wall. Tuesday, December 16, 2014, 12:43:48 PM, you wrote: > 7.3.2.4.1 > Sprinkler piping and fire detection devices shall be automatically > supervised where more than 20 sprinklers are on the system . > Would I be correct I do not require an air compressor in turn no low > switch either ? I just want to make sure I am reading it correctly . > I have done this in the past , I am just Second guessing myself . > Thanks . > Colin Carew > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkl > er.org -- Best regards, Charles mailto:[email protected] _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
