The Adventures of Duke Waters, Chapter 6

Duke let the phone ring four times before he picked up the receiver so he could have another sip of wine cooler and wipe his brow. It had to be over 100 degrees in Atlanta and it was only 10 a.m. Duke sat and quietly listened on the other end and heard my plea.

“Duke, I’m in Albany and need your help again with some slamming check valves.”

Duke never was much for small talk. He said “Johnny B, good to hear your voice. How are those air release valves working we installed last month on the coast?”

I said, “Great, the air is automatically venting from the pipeline and the pumps are running at peak efficiency. But, Duke, I’m working with your old pal Sam on the new Third Street Water Plant and have a battery of swing check valves here that are waking up the neighbors when the pumps shut down.”

Duke said, “OK, I’m not doing anything so I’ll fly in this afternoon and meet you at the job site.”

Duke was desperate to get out of town and away from the heat. Albany would be a refreshing change and a chance to catch up on old times with Sam. Sam had worked for Pro-Build Contractors for more than 10 years and had a PhD in fluid mechanics. Duke loved to talk fluids with Sam.

Duke drove to the airport in his red XKE. The car was crying with the top up, so when he got to the airport, he parked her in the hangar and put the top down. His Citation X was ready to fly, so he raced it down the taxiway, took off and left the scorching-hot air behind.

Sure enough, upon arriving at our job site, Duke heard the bang of the check valve from the parking lot. He found me at the pump motor control center room. Sam was talking to the plant operator.

I greeted Duke with a handshake.

“Sam told me that you and she must have started up 20 water plants over the years,” I said, raising an eyebrow.

Duke whispered, “Don’t go there. Let me tell you, Johnny B, she cares more about Newtonian fluids than me and mind your own damn business.”

“Duly noted,” I sheepishly replied as I moved aside so Duke could enter.

It had been years, but Sam greeted Duke warmly.

Without missing a beat, Duke said, “Samantha, I think we will be done here in an hour, and we’ll have time for some pasta at Tony’s.”

Sam got right down to business and said, “Duke, all we’re doing is lifting the treated water 20 feet and pumping it over to those ground storage reservoirs on the other side of the road. We run the four 24-inch pumps one at a time at 70 feet of head. Did you hear that slam?”

Duke replied, “Yes, I heard the slam, but that was nothing compared to the 60-inchers we heard slam in Puerto Rico back in the 80s. That slam was so violent, it made my ears ring and it spiked all of the pressure gauges on the pipe.”

“You’re right; that was a monster slam,” Sam said.

Duke added, “But the king of all slams I heard was from the closure of a blast valve.”

“What’s a blast valve?” Sam asked.

He explained, “I once worked on these special ventilation lift check valves back in the 60s for installation on the secret NORAD government facility in Colorado. When they sensed a nuclear strike, they were designed to close using a blasting cap and a high pressure air cylinder and coil spring in 10 milliseconds and then withstand the shock wave of an atom bomb.”

“Damn, that’s fast,” I said.

Duke went on. “The government inspectors wanted to witness a closure at the factory so we took this 20-inch blast valve outside and detonated the fuse,” he said. “It closed with such energy and noise, it blew out a window of a parked car and then the fire department rushed over thinking there was an explosion at the factory. As I said, that was a hell of a slam.”

“Sounds like it to me,” I said and added, “But we still need to solve today’s slamming problem.”

“Johnny B,” Duke said. “I thought we had a long talk about conventional swing check valves, remember? Levers, weights, air cushions?”

“Duke, I certainly remember our little talk about check valves with levers and weights. I also remember how the weight sometimes limits the valve opening to 20 degrees and increases the amp draw on the pump motor. So, on this project, I called Sam and had her add air cushions to the swing check valves.”

Sam jumped in, “I told John that air cushions are not an end-all to check valve slamming problems and tried to explain that you cannot slow down the closure of a slamming disc using a compressible fluid like air. But he insists on believing all of that marketing gobbledy-gook that manufacturers publish.”

“Careful now, Sam,” Duke said, “Marketing makes the world go ’round.”

I asked, “Well, then, who are you supposed to believe?”

Duke responded with, “How about you believe the physics because physics never lies.”

I said, “OK, fine; what does the physics teach us here?”

Sam said, “Well, if you really want to slowly close that slamming disc, you need to use an incompressible fluid such as oil.”

I said, “I happen to know that you typically can’t add an oil cushion to a check valve with an air cushion because most swing check valves with air cushions have wimpy, small-diameter hinge pins. When an oil cushion is used, the hinge pin must be able to restrain the moment created by the full differential pressure across the disc, so a special heavy-duty check valve is required.”

“That makes sense” Sam said. “The hinge pin on this valve can barely hold up the lever and weight, let alone the enormous twisting forces caused by the differential pressure across the disc.”

Duke volunteered, “Well, I happen to know a quick solution here that I have seen work a couple of times in the past.”

I said, “I’m game, let’s have it.”

Duke explained, “As you know, this air cushion is designed to draw in air as the check valve opens and then slowly release the air through a flow control valve as the check valve closes. But as we saw, the water forces on the disc are extreme and simply compress the air, which in turn allows the disc to close anyway and cause a water hammer. In fact, the damn air actually slows down the disc just enough to allow the reverse flow to increase even higher and cause a bigger slam.”

Duke continued, “But if we can get the air cushion to close the check valve faster instead of slower, then we may be able to reduce the slam.”

Sam said, “I think I see where Duke is going on this. If we move the flow control valve to the other port of the air cylinder, the air in the cylinder will get compressed when the check valve opens and will act like a spring to rapidly close the check valve.”

“Exactly,” Duke said.

So I re-piped the air cylinder by first switching the vent and the flow control valve on the two cylinder ports. Then, as suggested by Sam, I closed the flow control valve on the top port, which seemed intuitively wrong.

We asked for the pump to be cycled again and to my surprise, the slam was hardly noticeable.

I said to Duke, “Well you did it again and all I need now is a schematic of this setup for the instruction manual.”

“I’ll send you a sketch with my bill.” Duke replied.

“Can’t wait,” I said.

“Sam,” Duke said, “Shall we?”

I’m sure they were on their second glass of Chianti before the plant owner knew we were gone.

Up next in the series: Duke and Johnny B. troubleshoot a problem at a water plant: a valve closed but the pump continued to operate, ruining it.

John V. Ballun, president and CEO of Val-Matic Valve, is a regular contributor to VALVE Magazine.