Low maintenance pumping of thixotropic paste

At Quest International's Yeast Factory, Menstrie, Clackmannanshire a Watson-Marlow Bredel SP65 hose pump has been in operation for more than six years, handling a thixotropic paste at viscosities up to 100,000 cP.

The paste produced from the yeast is abrasive with a high salt content, but pump maintenance has been largely confined to a hose change every 12 to 14 months.

In this application it is important that the performance of the SP/65 hose pump remains consistent, unaffected by changes in media viscosity or by the presence in the paste of varying quantities of entrained air. A gentle, low-shear pumping action is equally necessary to avoid risk of structural alteration to the product.

At Quest International, the pump delivers savoury paste at a normal operating temperature of 60C from a tank to a packing head, operating for 16 hour periods several times a week. Operating over a speed range of 2.5 to 15 rev/min, output is 1000 to 6000 litre/hour.

Hygiene and contamination prevention are other major considerations. The SP/65 pump installed at Quest International is a modified version designed specifically for cleaning-in-place. To prevent the flow of cleaning agent being impeded by a partially compressed hose element during the CIP process, in the modified pump the two pressing shoes can be automatically disengaged and retracted, permitting high velocity, unobstructed circulation of cleaning fluids.

With no glands or seals to leak or clog and with the product enclosed within the hose element throughout the pumping process, risk of product contamination from external sources is totally eliminated. Sanitary hose connections are fitted.