Mounting a knife gate valve

[Hokiemjs]

Good evening. Here is my question that I would love some advice on:

I am working with a civil engineer who has selected a knife gate valve to be installed on the flange of a pipe in an earthen dam. The pipe flange is on an angle parallel with the face of the dam. I have been asked to provide a detail to mount the knife gate to a concrete pad. I plan to use epoxy anchors. What I don't know is what the forces would be I would need to design for and how to make the connection from the body of the valve to the anchor bolt.

For reference the valve is an orbinox model ET Series 20. I have contacted the manufacturer but have not been called back.

Any thoughts? Any way I can cross post this to civil since those guys might know more about valves? I started here since my background is structural and it seems to be a structural question.

Thanks for your time!

 

[Ron]

The loads you'll need for your anchors are likely the pressure loads on the face knife when the valve is in the closed position. If the pipe is from a pump source, then the pressure would be the maximum head from the pump. If the pipe is in a gravity flow, then the differential head from the maximum water level to the elevation of the centerline of the closed knife blade would be used.

 

[Hokiemjs]

Thanks Ron. That sounds reasonable. The other load case I thought about was when you are in the process of opening or closing the valve. If you have water rushing through the pipe and you are turning the handle to close the knife, I would think that there would be some resistance to that action. The water and debris would be beating on the plate perpendicular to the plate, but the screw/actuator is parallel to the plate (perpendicular to the flange of the pipe). I would think that there would be a shear on the anchor bolts then, too, in addition to the pressure head. Does that sound reasonable to you? Any idea on how to estimate that force?

 

[SlideRuleEra]

Hokiemjs - Usually a knife gate valve that is hand actuated is geared down so that it takes a fair amount of time to close. The slow closing process makes the pressure changes, like water hammer, less of a problem. If you had a very long pipe leading to the value and an electric actuator sometimes the closing time has to be intentionally slowed.

Pressure problems during closing are more common on quick-closing, quarter-turn valves, like a butterfly valve.

Since a knife gate valve is thin and usually not too heavy, it is often sandwiched between two pipe flanges. The mounting pad can support one, or both sides of the pipe next to the valve. The details depend on the size and structural properties of the pipe.

Is this the spec sheet for your valve:

http://www.americancontrols.com/images/pdf/SER20NEW.PDF

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Hokiemjs]

SlideRuleEra - Thank you. Yes, that is the spec sheet. I see that the knife gate can mount to the flange of the pipe (The pipe is for outlet from a dam, so there is pipe on one side, and nothing on the other that I am aware of). The concern I had was that the knife gate will be so far down in the water (maybe 30-40 feet) and the screw will be so long to get back to the work platform where you can turn it, that the body of the gate should probably be mounted to something rather than just relying on that circle of bolts at the flange. Maybe I'm over-thinking it, and the bolts around the flange are sufficient to hold it and the screw can just be extra long. Just trying to get some thoughts from others as to what they see going on here.

 

[DamsInc]

The other load case I thought about was when you are in the process of opening or closing the valve. If you have water rushing through the pipe and you are turning the handle to close the knife, I would think that there would be some resistance to that action.

Consider the forces that occur when the valve gets jammed up, so the operators grab an extra long pipe wrench and a few other guys to try to force it.

 

[Hokiemjs]

DamsInc - Yes, that was the other concern. Bound to happen (no pun intended)

 

[SlideRuleEra]

Hokiemjs - The flange bolts are the best way to hold the valve. You want the valve to be part of the piping system, not a structural member that interacts with the piping. You probably don't have a problem, even the heaviest hand operated valve on the spec sheet is 638 pounds, for the 24" size.

This looks like a general purpose valve, you do need to talk the valve manufacturer about installing it underwater - I doubt if that is a good idea. Knife gate, and other valves need maintenance from time to time. The normal practice for underground applications is to put the valve in a water tight concrete "valve pit" so that it is accessible.

Also, if there are problems with the valve there should be a way to isolate it... without having to drain the reservoir. In the electric utility business this is done by incorporating what are called "stop logs" that can be manually placed in dedicated slots in the dam to isolate the valve from the reservoir.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Signious]

I can remember doing valve-thrust calcs in school for this exact situation. If you still want some guidance on doing the calcs let me know and I'll pull out a few books & write something up. If I remember correctly, Jannas, 'Design of Fluid Thermal Systems' touches on this, as well as Cammeron Hydraulic Data.