PROCESSING TECHNOLOGY 33
a highly abrasion-resistant, chemical inactive and durable material, which is approved for shaft seals in pharmaceutical applications. Carbon/stainless steel shaft seals are unsuitable as carbon abrasion could interfere with the WFI’s sterile status.
Te most challenging aspect of shaft seal operation in WFI systems is the fact that the purity and the relatively high temperature of the liquid combined cause poorer lubrication of the seal faces. Tis may induce noisy friction and wears heavily on the shaft seal, reducing the life of this essential component. In this respect, choosing a pump with a double shaft seal is the optimum solution. A flushed double shaft seal with seal water offers the following advantages:
Improved lubrication. Better protection against dry
running. Efficient cooling of the shaft seal. Increased operational safety
by further safeguarding against contamination. Significantly increased lifetime of the shaft seal.
Te initial cost of a pump with a double shaft seal is higher and so are the operational costs due to the consumption of cooling water for seal flush (typically 4-5l/hrs. However, the value of the above- mentioned advantages often more than compensates for the difference because costly system downtime can be avoided. So a double shaft seal solution may prove to have a positive impact on the reliability of the entire WFI production system. .
Operational safety WFI systems invariably demand that pumps are fully drainable to ensure a reliable SIP (sterilisation-in- place) operation. Vertically installed aseptic pumps offer unmatched drainability and high operational safety compared to traditional pump systems.
Where traditional horizontal pumps must be fitted with separate drain valves, which add a dead leg on the
casing, the self-draining vertical pump has been designed without these potential sources of risk, allowing for a much safer production of WFI.
The beneficial control Water for injection must be constantly circulated in the distribution loop in order to maintain its sterile properties. Tis places great demand on the pump in terms of maintaining the correct pressure and flow at all times – even when water is being drawn from the system in large amounts at one go. Tis can either be done by operating the pump at constant full speed or – preferably – by adjusting the speed according to the required flow by means of variable speed control.
Te use of pump control is considered best practice in WFI systems as it offers a number of benefits: reduced energy consumption; optimised system performance; increased comfort, eg less noise.
Today, pumps can be equipped with integrated frequency drives to ensure an optimum match between the frequency drive parameters and the actual pump requirements. Tis further reduces the time for parameter setting and significantly minimises the risk of incorrect settings. Moreover, if the pump features external couplings between the motor and the pump shaft, the frequency drive and the motor can very quickly be replaced in case of maintenance – without having to re- sterilise the WFI system.
In WFI systems, it is recommended to choose pumps that have been certified according to the EHEDG standard for cleanability (CIP) and sterilisability (SIP). All wetted metal parts of the pump must be delivered with material traceability certificates (EN 3.1.) and all non-metal parts must be delivered with a FDA conformity declaration.
Mogens Roy Olesen, Market Segment Director, Grundfos, Århus, Denmark.
www.grundfos.com
Circle 33 or ✔ at
www.scientistlive.com/elab
Below A fully drainable pump.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36