News Archive

Issue 4 April 2008

Selection + Pricing = Service life…

Many thanks for your questions regarding extending your pumps’ capabilities to handle those applications that you find expensive or troublesome to run: typically, higher pressures with slurry type product.

Noticeably, many of your problems arise from being tempted by price: the initial lower cost option, say, of a single stage progressing cavity pump or a lobe pump being significantly lower than that of a two or three stage PC pump.

To help you see why the additional payment for the extra pumping chambers or stages is value for money on high pressure and /or slurry applications it is worth revisiting some of the PC pumps’ design characteristics.

The progressing cavity pump is a single helical rotor, rolling eccentrically in a double threaded helix of twice the pitch length. In doing so it forms a series of cavities, 180 deg apart, that progress from suction to discharge. As one cavity diminishes, the opposing cavity is increasing at exactly the same rate; so the sum of the two discharges is constant.

This rotation represents one total pumping chamber or stage, the pumps seal line running from start to finish, measured along the total length of the helix pitch of the single rotor stage. (This is one reason why Robbins & Myers Moyno rotor geometry has a steeper pitch angle than many of our competitors.)

This seal line is responsible for preventing slip or backflow within the pump; however, each stage has a maximum pressure capability: if exceeded, or neared, another pump stage should be added.

Many of your wear or failure descriptions are due to backflow, combined with high pressure and abrasives. This combination will mean wear to your pump will be severe and quick.

The answer is to increase the number of pump stages; but how do you know, when reviewing quotations, you are being given the right number?

Check out your next pump quotation

The number of stages you might require for your PC pump for longest life and lowest maintenance costs.

• Clean fluids 75psi/stage
• Abrasive applications 20psi/stage

As in all pump selections judgment is required, if you are near the pressure limit of a single stage, but the duty cycle is low, say only a few hours per week, then you could use a single stage pump as service life would still be acceptable.


Product News
Further pump designs that can extend your sites’ pumping capabilities:-

PowerFlow Pump- Metal Rotor and metal stator!
Main applications-

• Highly viscous
• Abrasive or corrosive fluids
• Where stator elastomeric materials would fail due to chemical or temperature

These categories of users are benefiting from the unique Power flow metal stator design!

• Adhesives and sealants
• Paints and coatings
• Filled asphalts, coal tar epoxy
• Polymers and resins
• Plastics and synthetic rubber
• Pastes and gels
• Soaps and detergents
• Petroleum: Slop oil, residuals
• Paper: Hot starch, de-inking sludge
• Semi-sanitary services
• Chemical and industrial waste

The PowerFlow is a prime example about what the “Inside Story” e-bulletin service is all about: correct pump selection.

Select this pump only for high viscosity products, typically those listed above. Why? Because the fit between the hardened tool steel and stainless rotor and stator is no longer transitional; actually, it’s a clearance fit, at odds with the traditional rubber stator pumps, I hear you say!

The benefits for you are, however, increased chemical and temperature pump capability. Additionally, rotor and stator life for non-abrasive fluids can be extended by ten times!

Pump performance summary:
Flows to 400Gpm
Differential pressure to 1,500 psi
Viscosities 100 cps to 1,000,000 cps
Temperatures to 500 deg

An interesting and fairly unique pump, in the right application, will exceed your expectations.

IFAT 2008 Exhibition- Munich
See you there! Our location is WEF Pavilion, Hall 4, Stand No 5018.

If you should require further information regarding pump selection in general, or for PowerFlow, please do not hesitate to call T 023 80760000.

Best regards

David Johnson
Business Development Manager