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AxFlow's pump technologies

Monday, June 1, 2009

The choice of pump technologies which AxFlow Group companies provide to the chemical and petrochemical industries is comprehensive and encompasses Rotary Lobe, Progressive Cavity, Metering/Dosing, Gear, Vane, Hose and AODD pumps.

Rotary Lobe pumps

Rotary lobe pumps employ timing gears which eliminate contact between the rotors and enables them to handle non-lubricating fluids. There are various designs of rotor, including bi-wing and multi-lobe options. Providing low shear and gentle handling of the liquid, thereby minimising product degradation, rotary lobe pumps are also easy to clean in place (CIP) or strip clean between operations for batching applications.

The circumferential piston pump is further development of the rotary lobe pump design. In this design the arc-shaped rotary pistons, or rotor wings, travel in annular-shaped cylinders machined in the pump body. The resulting long sealing path reduces slippage and produces a smooth product flow without destructive pulses or pressure peaks, and without the need for valves or complex parts.

Metering Pumps

Reciprocating positive displacement process (metering) is a proven method for the in-line proportioning and dosing of liquids and provides the highest levels of accuracy and repeatability available. The factors affecting the choice of a metering or dosing pump as opposed to other types of pumps are normally associated with precision over a range of flows and the fact that the capacity is not influenced by pressure fluctuations within the process.

In a process where an ingredient has to be added accurately to a varying main flow, the proportion can be maintained by speed adjustment, whilst any corrections necessary to maintain product quality can be made by adjustment of stroke length. This means that the metering pump can be finely tuned to the requirements of the system. For toxic materials or exacting applications where security and safety are priorities, a diaphragm pump-head is usually the first choice. For less demanding applications, a plunger pump-head will normally suffice.

Peristaltic Pumps

The peristaltic hose pump can also be considered for applications where media needs to be added to a processing system with high levels of accuracy and repeatability. Using the principle of moving the media through a hose by squeezing the hose between rollers or shoes at specific intervals to create a positive displacement action, any possibility of contamination of the pumped media is wholly eliminated. Applications for this pump are diverse and many, including the addition of sensitive solids, dosing of flavours and syrups, and even removal of waste. Capable of dry-running and self-priming, the pump provides that all-important requirement for low shear.

Progressive Cavity Pumps

For duties where media needs to be moved at low velocities, progressive cavity pumps also provide low shear characteristics. Employing a single rotor to move fluids in a continuous flow, the performance of progressive cavity pumps is largely down to the geometry of the rotor and the stator in which it turns. The materials from which these two elements are manufactured need to be matched to the pumped media in which they come into contact. In order to achieve life cycle costing goals the rotor and stator need to offer high levels resistance to aggressive fluids, which brings into play rotor geometry and material specification.

Gear Pumps

Gear pumps are fixed displacement technology, meaning they pump a constant amount of fluid for each revolution. This pump type uses meshing gears to pump fluid by displacement and is one of the most common types of pumps to be used in chemical installations for pumping fluids with a certain viscosity and also for hydraulic power applications. The internal gear pumping principle uses two rotating gears which un-mesh at the suction side of the pump to create voids which allow atmospheric pressure to force fluid into the pump. The spaces between the gear teeth move the fluid on either side of a crescent to the discharge side and then the gears re-mesh to discharge the fluid. There are two main variations, these being external gears which use two external spur gears and internal gear pumps which use an external and an internal spur gear. The rigid design of the gears and housing allow for very high pressures and the ability to pump high viscosity fluids.

Vane Pumps

An alternative technology to the gear pump is the sliding vane pump. This pump operates through the use of a number of vanes that slide into and out of slots in the pump rotator when the pump is rotating. The vanes move outward from the rotor and ride against the inner bore of the pump casing, in the process forming pumping chambers. As the rotor revolves, liquid enters the pumping chambers from the suction port. The liquid is transported around the pump casing until it reaches the discharge port where it is forced out into the discharge pipe. This type of design almost eliminates slippage, meaning that the pump's high volumetric efficiency is maintained.

Because the self-adjusting sliding vanes continuously allow for wear, sliding vane pumps are able to maintain near-original efficiency and capacity throughout their working life. The pump speed also does not need to be increased over time, making sliding vane pumps inherent energy savers. In the event of the sliding vanes wearing out or becoming damaged, replacing them is a simple and quick operation that does not require any special tools.

AODD Pumps

In any review of pumps for the petrochemical and chemical processing industries, the air operated double diaphragm (AODD) semi-positive displacement pump cannot be overlooked as the number of applications for it is simply enormous. This is because it can transfer almost anything and it is ideally suited to operation in hazardous areas. The absence of close fitting parts allows solids to pass through the pump without harm, whilst abrasive and viscous products can be pumped without any damage to the fluid characteristics.

Air-operated double diaphragm pumps (AODD) use compressed air to act upon the diaphragm and draw the liquid media into the pumping chamber and then eject it, so there are no rotary parts involved. When running, the dynamic components that come into contact with the fluid are the two diaphragms which are connected by a common shaft, the two inlet valve balls and the two discharge valve balls. The diaphragms act as a separation membrane between the compressed air supply and the fluid. Driving the diaphragms with compressed air, rather than the shaft, balances the load on the diaphragm which removes mechanical stress and therefore extends diaphragm life. The valve balls open and close on the valve seats to direct the flow.

AxFlow recognises that many application and operating environments place great physical demands on the pumps and their components. Materials used in pump construction always reflect the nature of the application, thereby ensuring that the effects of wear, corrosion and/or erosion are minimised. Where pumps have to work in hazardous areas, AxFlow is able to address and satisfy the requirements of ATEX accreditation.

The AxFlow Group, headquartered in Sweden, is the largest distributor of positive displacement pumps in Europe. With operating companies in more than 20 countries and a Distribution Centre in the Netherlands, it is able to ship pumps and other equipment from stock to customers within 48 hours anywhere in Europe. In order to be a true provider of fluid handling solutions the Company also includes mixing technology as well as instrumentation and analysis equipment within its product portfolio.

Issued on behalf of:
Olga Krejci Halkovova
AxFlow Holding AB
Wenner-Gren Center
Sveavaegen 166, Floor 14
SE-113 46 Stockholm
Telephone +46 8 545 476 79
Telefax +46 8 545 476 89

Bryan Orchard
Orchard Public Relations Ltd
Direct Tel/Fax: +44 (0) 1420 588194

AxFlow is active all over Europe and specializes in the marketing, distribution and provision of a complete sales engineering service for high quality, market leading fluid handling equipment. AxFlow's high standards of technical competence, service and integrity have contributed to steady growth since its establishment in 1989 and form the basis for future development. AxFlow represents world leading manufacturers of fluid handling equipment, and together we offer the highest value to customers. AxFlow's philosophy is to continue to enhance the range and scope of services, and to offer customers full commitment and value from one source. The AxFlow Group has an annual turnover of EURO 140 million (2008) and 400 employees and is a subsidiary of Axel Johnson International AB, Stockholm, Sweden.

Axel Johnson International markets and distributes components, systems and customer related solutions to industrial companies, local distributors and agents. The company consists of five business areas: Forankra, AxFlow, AxIndustries and AxImage. The group of companies has an annual turnover of EURO 640 million and is represented in some 20 countries in Europe. Axel Johnson International is a part of Axel Johnson AB, owned by Antonia Ax:son Johnson and family.

For more details contact
Olga Krejci Halkovova