Bearing pad size under 24" valve....
Bearing pad size under 24" valve....
(OP)
Good evening,
I have a question about an application of a bearing pad. We have an application where a 24” ball valve in a pump station is mounted to a concrete pedestal. The ball valve is located “in-line” between a large pump and a pipe header distribution system. We are suppose to use a bearing pad and limit the compressive stress on the pad to no more than 12 psi.
Based on the Dead load of the valve assembly and the some contributory load of the surrounding appurtenances (15,100 lbs) I have calculated a required minimum baseplate and pad size of 36” x 36” square (11.65 psi).
The engineer is now telling me that there is a startup pressure on the closed valve of 61 psi – this pressure is relieved as the valve is opened and the pump continues to run. He says that an overturning moment is induced in the valve base support and thus creates an additional compressive force on the bearing pad. With a calculated approximate force of 27,500 lbs on the closed valve (61 psi x area of a 24” dia pipe) and a moment arm from the top of the support to the centerline of the load equal to 29.5 inches, the design “blows up” and a bearing pad could never work.
It seems to me that any horizontal force applied to the closed valve would first go into the surrounding pipe and pump supports before it is transmitted through the valve bearing pad and into the valve support.
What guidance can you give me to help me limit the applied stress in the bearing pad to 12 psi?
Is it even reasonable to limit the stress in the pad to 12 psi in such an application?
Thanks in advance for your help.
I have a question about an application of a bearing pad. We have an application where a 24” ball valve in a pump station is mounted to a concrete pedestal. The ball valve is located “in-line” between a large pump and a pipe header distribution system. We are suppose to use a bearing pad and limit the compressive stress on the pad to no more than 12 psi.
Based on the Dead load of the valve assembly and the some contributory load of the surrounding appurtenances (15,100 lbs) I have calculated a required minimum baseplate and pad size of 36” x 36” square (11.65 psi).
The engineer is now telling me that there is a startup pressure on the closed valve of 61 psi – this pressure is relieved as the valve is opened and the pump continues to run. He says that an overturning moment is induced in the valve base support and thus creates an additional compressive force on the bearing pad. With a calculated approximate force of 27,500 lbs on the closed valve (61 psi x area of a 24” dia pipe) and a moment arm from the top of the support to the centerline of the load equal to 29.5 inches, the design “blows up” and a bearing pad could never work.
It seems to me that any horizontal force applied to the closed valve would first go into the surrounding pipe and pump supports before it is transmitted through the valve bearing pad and into the valve support.
What guidance can you give me to help me limit the applied stress in the bearing pad to 12 psi?
Is it even reasonable to limit the stress in the pad to 12 psi in such an application?
Thanks in advance for your help.





RE: Bearing pad size under 24" valve....
Here is an example, where the valve manufacturer is calling out 3000 psig:
http://www
The maximum loading is not at startup or when the valve is opened. The maximum loading would probably be when the pump is operating and a power failure occurs causing a quick shutdown.
In other words, the maximum forces are caused when you have changes abrupt changes in flow. To minimize these maximum forces, the engineer will use slow closing valves, spring loaded check valves, etc.
The pressure in the pipe is not going to increase the pressure on the bearing pad.
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
36" square seems a bit large to me. 15,000 pounds is a lot - perhaps you need some intermediate supports on the piping also? Maybe he is interested in keeping the pressure on the foundation below 2,000 psf?
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
RE: Bearing pad size under 24" valve....
With respect to the longitudinal force - moment issue, I would respectfully tell your engineer to go back to school. Simply put, if the valve was an end cap, where would the end load go? It is handled by the longitudinal stress in the pipe. None, yes, none of it goes into the pad. This is easy enough to test. Take a household garden hose. Put a spray nozzle on it. Turn on the water. Close the spray nozzle. Set it down. Does the end load on the closed spray nozzle do anything? Just because you have a system about 36 times larger doesn't change the way the reaction works.
Actually, simply deriving the longitudinal stress from a free body diagram proves this: The load due to pressure times area which you've already calculated is carried by the cross sectional area of the pipe, or pi*2*r*t. So force over area is P*pi*r*r/pi*2*r*t = P*r/2*t. Look familiar? (The hoop stress formula is derived in the same way, just take a unit length of pipe, cut it in half and look at the force/area.)
By the way, you would get a whole lot more exposure to piping engineers at forum378: Piping & fluid mechanics engineering: Piping & fluid mechanics engineering.
jt
RE: Bearing pad size under 24" valve....