Pressure Relief Valve on a Force Main

[Builder604]

I have a project where we have a pump station that will pump over a hill and then down to a dip at a directional bore under a creek and then to the discharge MH. The discharge MH elevation is lower than the pump station. Our initial thoughts are to install a Pressure relief valve/back pressure valve at the discharge point. This valve would keep the valve closed and pipe full when set to the static pressure between the high point and the valve. The pump would TDH would then be based on the friction head of the full length of pipe, the static head from pump to high point and static head from pressure relief valve to high point. Does anyone have any input on how well a pressure valve would work for a force main application like this? We are concerned with clogging.

 

[bimr]

Relief valves are not generally recommended on sewage applications for the reason you mentioned. Consider installing a manual valve to allow air to be removed on startup. Another suggestion is to maintain a flow velocity of approximately 3.5 ft/sec to force the air out.

 

[nondimensional]

Draw a system curve from pump station to the high point only.

Draw a second system curve from pump station to final discharge manhole ignoring the high point.

At your rates flow, whichever gives you highest head is your pump TDH. If this happens on the first system curve then add a vent about fourth of the pipe diameter at the high point. If this happens on the second system curve, add an automatic sewage combination air valve at the high point.

 

[MortenA]

Watch out for slack flow