PIPING PROBLEMS P059
THE SUCTION PIPING
Air is entering the suction piping at some point.
- Air is entering the stuffing box between the pump sleeve and shaft. Many times this gasket is left off when converting from packing to a mechanical seal.
- Air is being pumped into the suction piping to reduce cavitation problems
- Fluid returning to the sump is being aerated by too far a free fall.
- The fluid is vortexing at the pump inlet because the sump level is too low.
- Air is coming into the system through valves above the water line or gaskets in the piping flanges.
- The liquid source is being pumped dry.
- The vapor pressure of the fluid is too close to atmospheric pressure. When it rains the drop in atmospheric pressure causes the inlet fluid to vaporize.
- The gasket that seals the halves of a horizontally split case must penetrate the face of the stuffing box if a mechanical seal is installed or there will be leakage at some point in the stuffing box near the face.
There is a problem with the piping layout.
- There is too much piping between the pump suction and the source tank. You may need a booster pump.
- There is an elbow too close to the pump suction. There should be at least ten diameters of pipe between the elbow and the pump suction.
- A piece of pipe of reduced diameter has been installed in the suction piping.
- The sun is heating the inlet piping. It should be insulated to prevent this problem.
- Piping was added on the inlet side of the pump to compensate for a piece of equipment that was installed in the shop.
- A piping to pump reducer has been installed upside down causing an air pocket. Concentric reducers can cause the same problem..
- The pump capacity is too high for the tank volume.
- Multiple pump inlets are too close together.
- The pump inlet is too close to the tank floor.
- The suction lift is too high.
- A gasket with too small an inside diameter has been installed in the suction piping restricting the liquid flow.
- A gasket in the suction piping is not centered and is protruding into the product stream.
- A globe valve has been substituted for a gate valve. The loss of head in a globe valve is many times that of a gate valve.
- Two pumps are connected in series. The first pump is not sending enough capacity to the second pump.
The piping inlet is clogged
- A filter or strainer is clogged or covered.
- Intermittent plugging of the suction inlet. Loose rags can do this.
- A foot valve is stuck.
- A check valve is stuck partially closed
- A small clam or marine animal cleared the suction screen, but has now grown large on the pump side of the screen.
- If the suction is from a pond or the sea, grass can be pulled into the suction inlet.
The piping diameter has been reduced
- The suction piping collapsed when a heavy object either hit or ran over the piping.
- Solids have built up on the piping walls.
- A liner has broken away from the piping wall and has collapsed in the piping.
- A foreign object is stuck in the piping It was left there when the piping was repaired.
- The suction is being throttled to prevent the heating of the process fluid. This is common with fuel pumps where discharge throttling could cause a fire or explosion.
THE DISCHARGE PIPING
- Extra piping has been added to the system to accommodate extra storage capacity.
- A bypass line has been installed in the pump discharge increasing the capacity.
- Piping or fittings have been removed from the discharge side of the pump reducing piping resistance.
- A globe valve has been substituted for a gate valve. This will increase the resistance in the piping.
- Solids building up on the piping inside wall will restrict flow.
- A check valve is stuck partially closed.
- An orifice has been installed into the piping to restrict flow or to create a false head.
- The piping was collapsed by a heavy object that hit the outside of the piping.
- The discharge valve is throttled too much.
- There is a restriction in the discharge piping.
- Extra pumps have been installed into the existing piping.
- Units in the discharge piping should not be shut off, they should be by-passed.
- Be sure to consider the siphon affect of piping extending into the top of the tank when calculating the total head.
- Two pumps are in parallel. The larger one is shutting the check valve of the smaller pump.
- Two pumps are in connected in series. The first pump does not have enough capacity for the second pump.
- They should be running at the same speed with the same size impeller.
- The pump discharge is connected to the bottom of the tank. The head is constantly changing.
- The pump is acting as an accumulator, coming on when the tank level drops.