How to upgrade an old centrifugal pump?

If you have an old centrifugal pump that no longer meets the current application requirements (operating conditions are slightly greater than the previous requirements) and does not operate as trouble-free as I would like, should I buy a new pump or upgrade the original pump? How to upgrade an old centrifugal pump?

• If you find that your current centrifugal pump does not meet your application requirements and does not operate as trouble-free as you would like, and you have checked that:

1) All internal tolerances are correct.
2) There is no excessive pipe strain.
3) The clearance between the open impeller and the volute or backplate has been adjusted to the required position after the pump has reached operating temperature.
4) The pump and driver have been aligned.
5) The rotor components have been dynamically balanced.
6) The wear ring clearance is as specified by the manufacturer.
7) The pump is running at the correct speed, in the correct direction and with the correct impeller size.

You may have to buy a new centrifugal pump, or you may need to consider upgrading your existing pump to get the performance and reliability you need. This requires a thorough and detailed evaluation and then a sound decision.

• If you are considering upgrading an existing pump, you can start with the following:

1) Modifying the impeller diameter can get your pump closer to the best efficiency point. Using similarity laws, you can predict the effect of impeller diameter trimming on pump head, flow, required net positive suction head (NPSHR), and power.
2) Converting to an impeller with a different specific speed will change the shape of the pump curve, power consumption, and required NPSH.
3) Changing to a heavy duty power end can prevent larger shaft deflections, and some pump manufacturers will provide you with the pump shaft diameter required to install a "C or D" frame adapter to eliminate pump misalignment problems.
4) Replacing the sleeve shaft with a rugged, corrosion resistant shaft will usually reduce or eliminate shaft deflection problems caused by running away from the best efficiency point (BEP). If your pump uses a mechanical seal, make sure you use a type that prevents fretting corrosion. Most original equipment manufacturer (OEM) seals will damage the shaft, which is one of the main reasons they provide sacrificial sleeves.
5) Reducing the overhung shaft length can solve many shaft deflection problems. You should be able to reduce the L3/D4 number to an ideal 15 to 20 by reducing the shaft length or increasing the shaft diameter.
6) Changing the wet end to a double volute configuration will allow the pump to operate in a larger window without the danger of excessive shaft deflection.
7) You can drill a hole in the top of the stuffing box to increase stuffing box venting.
8) Change the flush or recirculation connection from the top liquid seal ring connection to the bottom of the stuffing box to ensure better fluid flow through the stuffing box. Try to get as close to the seal face as possible.
9) Increasing the stuffing box ID or using an oversized stuffing box can solve some long-standing sealing problems.
10) Converting the wet end of the pump (pump housing) to a centerline support may solve some pipe strain problems by compensating for radial thermal expansion.
11) Increasing the clearance between the impeller and the volute tongue can prevent cavitation problems (which can prevent impeller blade passing frequency and low frequency vibration problems).
12) Installing a sight glass in the bearing housing can help you maintain the correct oil level and prevent bearing overheating problems.
13) Replacing the bearing housing grease or lip seal with a bearing labyrinth seal or Inpro seal prevents water/humidity from entering the bearing housing and can prevent premature bearing failure.
14) Replacing the radial bearing retaining ring/snapping ring with a more secure retaining device can eliminate many problems associated with axial movement of the shaft.
15) Replacing the packing seal with a good mechanical seal can reduce power consumption and leakage of the pumped medium.
16) Replacing the integral mechanical seal with a split mechanical seal can shorten the time required to replace the seal and eliminate the process of disassembling the pump and sending it to the workshop that requires other trades to participate.