Swing Flex Check Valves Experience in Raw Sewage

[stanier]

Hi all,

My client is considering the use of a Swing Flex check valve , 30" diameter on raw sewage. Velocity upstream of the valve is 1.5m/s. Has anyone any good or bad experiences of this style of check valve. It has a reinforced rubber flap that moves through a short arc of 35 degrees.

The manufacturer claims it can be installed in the vertical however I am reticent to do this on raw sewage.

Is reverse velocity versus deceleration data available for surge analysis?

Yes, I have enquired of the manufacturer but would like some independent feedback.

 

[ccor]

Swing check valves are common for wastewater service. It sounds like you are describing a flap check, which I have only seen on much, much smaller force mains, say less than 6". Personally I would select a swing check with an outside lever, and locate it horizontally. "Ten States Standards" only allows ball check valves on the vertical run.

Most check valves close quickly enough on pump shut down so that surge pressures aren't a huge problem, however your velocity is high enough to put some thought into it. A large rotational mass (moment of inertia) on a centrifugal pump will produce a smooth velocity transition on pump shut down.

 

[stanier]

ccor,

hansk for the response. I actually do surge analysis for a living. I wouldnt use a conventional swing check valve with lever arm counterweight. The mass of moving parts makes sure it doesnt close quickly enough. (refer Thorley-Pressure Transients in Piping Systems). Ball check valves exhibit the worst reverse velocity vs deceleration criteria of all check valves and are a recipe for disaster.

The moment of inertia of the pump is a given with the sort of flows in question. I am not about to add a flywheel as this imapcts on the size of the pump chamber and hence the overall cost. The chamber is 25m deep.

It is specifically this rubber flap check valve I want a response about, from people who have installed and seen them in operation. They are available up to 42" , in the catalogue at least. Whether anyone has actually made one and put it into the field is a question to be answered.

 

[ccor]

stainer,

Way to sandbag on your transient design skills! I agree a ball check is not appropriate and a flywheel is probably not optimal. The swing check has the advantage of opening further for wastewater service and the outside lever and weights make it adjustable. For such a large system, a VFD is probably being used for start-up, you could also have it ramp-down at shut-off. I have heard of this being done but I have not done it myself, some though would have to be used with the pump off elevation.

Refer to "Pumping Station Design" by Sanks et al. I quote "The rubber clapper swing check valve has no outside lever, is not fully ported, and, hence, should not be used for raw sewage or sludge", also "This type of valve should not be used in raw sewage service because debris can pack above the disc and prevent the disc from opening", and "Manufacturer's that state that a check valve can be placed in a vertical pipeline are referring only to the springs or counterweights and ignoring the danger of deposited grit and solids, which can (and will) jam the valve."

Good luck with your project!