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Use of a PCM AV model Progressing Cavity Pump to Replace a Centrifugal Pump

PCM provided an API 676 compliant 25AV12 vertical progressing cavity pump, with the pump intake located 4 m below the mating flange.  The body is of 316L stainless steel while the rotor is duplex steel. 

The shaft is constructed of hardened steel with a Halar coating.  The stator elastomer is PCM 164 NBR, which is highly resistant to abrasion and with a wide spectrum of chemical resistance, in-house formulated and produced by PCM.  O-rings and other rubber components are NBR. A double mechanical seal (with SIC-SIC faces) was provided along with an API Plan 53B sealing system to ensure a long life in the presence of abrasive solids and to avoid any dangerous leak of H2S to the atmosphere.

PCM Case Studies - PCM AV model Progressing Cavity Pump to Replace a Centrifugal Pump

Challenge

The client was using an API 610 VS4 vertical centrifugal pump to intermittently empty an effluent tank.  The effluent was dirty (sometimes considered sludge), containing significant quantities of abrasive particulates.  Additionally, there was some H2S and other toxic materials which meant that using portable pumps to empty the tank was not acceptable.  

The particulate-laden material caused failures of the pump’s line shaft bushings, which was lubricated by the process fluid.  Adding an external lubricating system was not desirable.  Failures were occurring every two to three weeks of run time – one to three months of calendar time, depending on the frequency of the pump operation.  The high cost of maintenance was a concern to the customer.

Results & Benefits

The PCP which replaced the previous centrifugal pump ran for six months with no significant maintenance and no failures.  As per the contract, the pump was inspected after six months.  Some minor pitting was observed at the intake end of the stator.  The stator was replaced out of an abundance of caution. The used stator was kept in reserve for possible use as an emergency spare part in the future.  The pump has continued to run since that time with no further maintenance (as of another six months since the stator replacement).

The client expressed satisfaction with the level of service provided by PCM during the planned intervention.  The client commented that the PCM technician did a very good job and was very flexible with the timing of the job.  (While located geographically nearby, the technician’s base was in a different country.)

PCM Solution - PCM AV series

This case is an example of how a PCP can be successfully used to replace a vertical centrifugal pump in an application with high solids content, varying fluid properties, and low NPSH.  

The shaft design of the vertical PCP, combined with its low speed, operates very well in the presence of particulates.  No external lubrication is required for the shaft.  The PCP stator is well adapted to pumping sludge and other solids-laden fluids and can use an inlet strainer with a larger mesh size than would be possible with a centrifugal pump.  

PCP technology has also proven to be very effective in condensates recovery with the same success despite being more aggressive with elastomers by selecting an elastomer more resistant to light oil or condensates. For some customers, the PCP has become the standard in these applications.

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