You don't want to get me started on this subject - but here goes anyway. I will try to be nice. First, there are poor quality products out there in both categories. I will relay an experience of mine.
One of our sprinkler systems needs to be modified for a design change. The butterfly in the riser was closed but water was still at the remote point of the sprinkler system. The 2-inch drain was wide open and flowing but could not keep water out of the system. To do the work required closing the valves out on the main to allow replacing the riser valve. I have that riser valve under my desk and am using it as a foot rest. It was 6 years old at the time of failure. It might have failed before then and we didn't know it because it hadn't been called upon to perform. It failed because it had a plated disc. Any butterfly valve with a plated disc is designed to fail. Galvanic corrosion between the plating and the base material is the cause. They are listed this way but I don't know why. We won't install one. This one had holes eaten in the disc that allowed so much water to flow that a 2-inch drain was overwhelmed. We had this same kind of valve in our underground and interior fire mains - the plated disc kind - that failed after only a few years of service. Again, holes eaten in the disc. It cost a couple million dollars to replace all 110 underground and 24 interior valves. We single-sourced the replacement valve to get a good one. 20 years later most of them are still drop tight. Gate valves can have their problems too. Depending on the quality of water the inside can crud up on you and cause the valve to not seal well. This happens progressively over time. If in a riser, generally the 2-inch drain can handle the flow by. But, eventually, it will not seal well enough and the valve will have to be replaced. In the end you get what you pay for. If you want a butterfly valve in the riser specify a high-quality one and definitely not one with a plated disc. If you want a gate valve, most are probably ok but expect them to leak a little after being in service but not to the point of overwhelming the 2-inch drain, at least for their normal expected lifetime. Of course, all bets are off if you get a poorly made one. John Hoffman P.E. | Fire Protection Engineer | Facility Engineering Services, KCP, LLC - Burns & McDonnell Engineering | National Nuclear Security Administration's Kansas City Plant | Operated by Honeywell FM&T | 2000 E. 95th St | Kansas City, MO 64131 | ph 816-997-7213 | [email protected] From: "Chris Cahill" <[email protected]> To: [email protected] Date: 01/27/2011 09:29 AM Subject: Butterfly vs. Gate valves Sent by: [email protected] Anyone have evidence or reasoning why a BFV would be more prone to leaking past the seat when closed than a GV. I hadn't heard this before. But in the last week or so have heard from several independent sources the same concern. I'm try to figure out if there is something to it or passed down urban legend. I've never had a real preference. BFV a little cheaper and tampers are a little easier to deal with and take up a little less space in our typical valve rooms. But if they leak more often maybe I can form a preference. Chris _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
