Centrifugal Pumps Overhauling - Procedure To Dismantle

An OIL AND GAS INDUSTRY contains several different types of pumps including centrifugal pumps. In the next few sections, the maintenance of centrifugal pumps is explained. Here we will have a look at the procedure to strip, inspect and reassemble a centrifugal pump, forming part of the planned maintenance schedule onboard industries for the purpose of maintaining the equipment in optimum operating conditions.

Centrifugal Pump

The first section gives an overview of a typical centrifugal pump operation

Overview:

As we saw earlier; the centrifugal pump was developed in the mid-1800s, although it was used in a crude form before then. The main design change was by John Appold in 1851; he replaced the impeller straight vanes by curved blades.

The pump converts mechanical energy from the drive to kinetic energy, with this being transferred to the fluid as pressure.

This takes place due to the two main components of the pump: the impeller and the volute. The rotating impeller converts the input of mechanical energy to kinetic energy, while the stationary volute converts this to pressure.

The fluid to be pumped enters the pump through the suction pipe nozzle, where it is drawn directly to the impeller “eye" located in the center of the impeller. The impeller spins the fluid tangentially and radially with centrifugal force outwards. The curved blades create a low pressure at the eye that allows more fluid to be drawn from the suction nozzle to the impeller.

So basically, the pump operates on the transfer of mechanical energy from the drive motor from where it is converted to kinetic energy that is transferred to the fluid as pressure energy. The rotation of the impeller with its curved vanes draws the fluid from the suction nozzle; throwing it outwards, expelling it through centrifugal force from the discharge nozzle.

A sketch of a horizontal pump is shown below.

Removal of Pump for Inspection and Maintenance:

1. Isolate pump electrical circuit breaker on the main switchboard and attach a warning notice. (Do Not Operate-Men at Work).

2. Switch off and lock pump supply at its local supply panel. Attach a warning notice to pump the local supply panel.

3. Close suction and discharge valves, chain and lock handwheels.

4. Open pump suction and discharge pipe drain valves to bilge and when water ceases to flow; crack open the pipes/pump flange joints carefully to ensure that the pump has drained off and is safe for opening.

5. Fix a shackle to lifting pad eye above the pump and hang chain block; ensuring SWL of the block, slings and shackles are satisfactory.

6. Use a center-punch to match/mark coupling and casing, then remove the coupling bolts.

7. Disconnect, fix i/d tag and remove motor supply cables; taping over bare ends with insulating tape.

8. Connect shackle and sling to motor eye bolt and lift motor clear of the pump using overhead chain block. Lay motor on its side out of harm’s way, protecting machined surfaces on both pump and motor coupling halves against damage. (Cardboard and masking tape is a quick and efficient method.)

9. Disconnect all external fittings from pump casing e.g. cooling pipe, pressure gauge, oil reservoirs, and air cock.

10. Remove bolts from the top cover and remove the cover. Scrape off the old gasket and checkmating surfaces, and renew gasket on assembly. (A light smear of grease on gasket/faces)

11. The pump shaft with an impeller can be lifted out of the casing.

12. Dismantle the impeller, and remove the wear ring.

13. Remove the gland packing and disregard; replacing it on rebuild. Remember to cut ends of packing at 45° and stagger joints when repacking the gland.

Centrifugal Pumps Fitted on Board (Images Taken from National Center for Appropriate Technology Website)