News Archive

Issue 2 February 2008

5 considerations for pumping- Abrasive, shear sensitive and or high viscosity products.

Your main process and plant considerations are probably:-

Quality of pumped product: Unchanged
Pump reliability: Lowest running costs

Whilst progressing cavity pumps dominate this difficult product category, you will find many different pump designs operating in the field. The most important factor for selecting a pump for these arduous duties is correct selection - not brand, design or price - but matching your pump to the duty conditions exactly. If not, wear and tear, poor performance and pump failure will come round quickly, regularly and expensively.

Let’s have a look at the considerations you should be aware of for most pump types in order to achieve your goals. Examples are PC biased!

Remember it’s free to call, for further selection guidelines.
Tel: 023 8076000 or email rmsales@robn.com Please reference “inside story”.

Design Factors
1- You want the straightest and simplest flow path of fluid through the pump to achieve low velocity within the pump and low shear.
The flow-line in a PC pump is a straight line!

2- You want to eliminate product backflow or slip within the pump. Particularly at high pressures, backflow of the product can create rapid localised wear and shear damage to the product.
PC pumps utilise, in effect, an elastomers as the outer gear: this is a compression fit between the rotor and stator, creating a continuous seal line per stage.
This has the added advantage of making a PC pump suitable for pumping low viscosity and gaseous fluids, as well as high viscosity.

3- You want to select the best materials for abrasive duties. Pump manufactures offer rubber lined, hard metal and ceramic to resist abrasion, chemical and temperature.
You can probably find material match from most renowned pump manufactures.

The PC pump, however, wins due to a combination of stator and rotor material selection, plus low product velocity within the pump. Particles tend to imbed, and deform the stator rather than abrading it, the rotor being protected with, typically, a hard wearing coating.
Depending on chemical, temperature and pressure compatibility, a stator elastomers with a 50 to 70 durometer (Shore A), typically a high grade of natural rubber, provides the optimum balance of softness and resistance to deformation under pressure.
For the rotor, typically air-hardened tool steel, 55-58 Rockwell “C”, with either single layer or double layer of hard chrome plate, offers greatest abrasion resistance.

4- You want to think seriously about pump speed. Let’s be honest, you can get everything right, but if you increase the pump speed to purchase a smaller and lower cost pump, then you probably pay for that choice many times over. This generally applies to all designs of pumps.
As a guide, the ideal speed for a PC pump is probably below 350rpm for abrasive applications; where pump longevity is required, short batch operation is possibly around 600rpm. Get it wrong and you find PC pump wear for abrasive applications more closely proportional to the speed squared than it is to a direct relationship.

5- You want accurate metering or dosing of abrasive slurries, often falling into the non-Newtonian category; meaning pump speed selection is critical to ensure each cavity of the pump has been filled before the next pump cavity is offered to the suction. Getting this right can be a mixture of sum, experience and trial!
Your PC pump offers the advantage of accurate metering and dosing even when the pumped product changes viscosity dramatically: size and selected pump speed for the maximum viscosity and pumping accuracy will be maintained where other pump designs will lose pumping efficiency when viscosity drops to an extent that slippage occurs within the pump.

If you would like more information please do not hesitate to contact our team T023 8076000 or email scarter@moyno.com

To give you an idea of the pumping performance possible from a progressing cavity pump here are a few examples of what can be done-

Automobile repair compound
Dealing with viscosity in the range of 300,000 to 600,000 centipoises and highly abrasive. This is typical of many automobile body shop repair compounds which also contain chopped, extremely abrasive, glass fibre. To picture this fluid, appreciate that it’s designed not to run or sag!

Oil and water mixtures
For many pumps, pumping oils, particularly with any possibility of water present, would result in emulsification of the product. However, the average shear rate of a progressing cavity pump can be less than 100 sec-1 enabling pumping of oil and water mixtures without emulsification

Other pumped products in the difficult category that we are considering could include: sandy crude, coal slurries, waste sludge’s, polymers, drilling mud, tallow and grease, sealant, asphalt emulsions, paper stock, refractory mortar, gypsum, caulking compounds, margarine, sausage meat…

 

NEW – Product News.

Chopper Hopper, the ultimate process enhancer –
After years of in-depth grinding and cutting experience our design team have developed the well-named Chopper Hopper.

The best and quickest route to get familiar with this product is to view the video specially prepared for you on our website www.moyno.com. At the very least, it’s amusing!

Applications are-
Ethanol Production
Waste handling for disposal
Food processing, Fruit, vegetables including potatoes
Slaughter and rendering plants!

Obviously, I am looking forward to some of these sales visits. Seriously, I have included this product because once you see the video you will realise what I believe to be unique about its capabilities; and even though it’s not your everyday need, it’s worth knowing about.

Please call us regarding your pumping application for further information or advice – it’s free to talk! T 023 8076000 or
email rmsales@robn.com and please reference “inside story”

Very best regards
David Johnson
Business Development Manager