Alfa Laval Twin Screw Hygienic Pump, OS12 to OS46

Alfa Laval Twin Screw hygienic pump: what it is and how it is sized

The Alfa Laval Twin Screw pump is a hygienic positive displacement pump that moves product with two intermeshing, contra-rotating screws. Its main selling point is that one machine can handle both the process duty, where positive displacement pumps are normally used, and the cleaning-in-place (CIP) duty that is usually given to a centrifugal pump. Seven Star LLC supplies the Twin Screw pump in Oman and the GCC as an independent supplier in Muscat, and this page explains what the range covers so that you can send a complete enquiry.

The range is built from twelve sizes. The designations are OS12, OS14, OS16, OS22, OS24, OS26, OS32, OS34, OS36, OS42, OS44 and OS46, which are grouped in four families of three sizes. A series page like this one does not carry a single ordering code, so the size, seal arrangement and elastomers are chosen during selection.

Twin Screw pump technical specifications

The figures above are range limits. They do not all apply to every size at the same moment, so the duty point (flow, differential pressure, viscosity) must be checked against the size you intend to use.

How the Twin Screw pump moves product

Inside the pump housing the two screws turn in opposite directions without touching each other. Their threads and the casing together form closed chambers, and those chambers carry the liquid from the suction port to the discharge port in a steady axial direction. Because the liquid advances continuously rather than in discrete strokes, pulsation is very low and the product is treated gently. That is the reason these pumps are chosen for fluids that include soft particles or that are easily damaged by shear.

The same principle explains the strong suction behaviour. The pump offers good lift capability and a low NPSHr, which gives the designer more freedom in how the pump is installed relative to the tank and increases the share of product recovered from vessels. The pump can also be run at high speed for CIP flow, so a single pump can take the place of a separate centrifugal pump and its extra pipework, valves and control logic.

Construction and hygienic design of the Twin Screw range

The external finish is clean stainless steel. Profiled elastomers and the mechanical seals are fully surrounded by product, so there are few places where residue can sit. Materials are FDA-conforming, and the pump carries EHEDG and 3-A certification. For plants with hazardous zones, an ATEX version is available as an option.

The gearbox is also made of stainless steel. The timing gears are located between the bearings, which gives an optimised bearing span and a balanced load on the shaft assembly. Lower vibration and noise follow from this, and the oil chamber design improves lubrication of bearings and gears, which keeps the running temperature of the gearbox down.

Where the Twin Screw pump fits in a process line

The manufacturer positions the pump for dairy, food, beverage and personal care duties, including fluids that are sensitive, abrasive, or at either end of the viscosity scale. In a plant the Twin Screw pump normally sits between a feed tank and a downstream skid such as a heat exchanger, filler, mixer or homogeniser. Related pumps in the same hygienic family are the DuraCirc circumferential piston pump, and the OptiLobe, SRU and SX rotary lobe pumps. When the product does not tolerate any shear, or when the duty is only high viscosity at low flow, one of those may be the better answer, so we can compare options with you.

Selecting a Twin Screw pump: ordering checklist

• Product name, viscosity range (minimum and maximum) and whether it contains particles, with the largest particle size.
• Required flow rate and differential pressure at the pump, plus the suction conditions (lift, tank level, line losses).
• Process temperature and the CIP temperature and chemicals the pump will see.
• Shaft seal arrangement: single, single flushed, or double, and the barrier or flush medium where one is used.
• Seal face pairing (silicon carbide / silicon carbide or silicon carbide / carbon) and elastomer: EPDM, FPM or FFPM.
• Port connection standard, since a wide range of port specifications is offered.
• Need for ATEX, hydrostatic test certificate, or hygienic documentation.
• Drive: bare shaft, or complete unit with gear motor, and power supply details.

Installation, commissioning and maintenance

Because the Twin Screw is a positive displacement pump, the discharge line must never be closed against the pump, and a pressure relief device is a normal part of the installation. Set the direction of rotation before start-up; the manufacturer describes a procedure for reversing the flow direction and setting the screw timing, which shows that the pump is designed to be reconfigured on site.

Service is meant to be quick. The cartridge seal is front-loading and self-setting, so it can be replaced with the pump left in the line. Service kits are available for single, single flushed and double seals. The timing gears are reachable with the pump in place, so screw retiming does not need the gearbox oil to be drained, the coupling removed or the motor taken off. Keep a seal service kit and a set of elastomers as spares, since these are the wear items you are most likely to need.

Typical applications in Oman and the GCC

Twin Screw pumps and similar hygienic pumps are used in the region wherever food and beverage and personal care products are made: dairies, juice and drinks plants, edible oil and sauce lines, and cosmetics or detergent filling. These plants run in hot, humid conditions with frequent washdown, so a stainless external finish, sealed bearings and easy access for cleaning are practical advantages. The twin screw principle is especially useful where one line carries several products with different viscosities, because one pump can serve all of them and also pump the cleaning solution.

Seal and size summary

Information to send with an RFQ

• Twin Screw pump size (for example an OS size), if known, or the nameplate details of an existing pump.
• Product, viscosity and temperature data for the Twin Screw duty, and the CIP regime.
• Flow, pressure and suction conditions.
• Seal and elastomer preference, and any flush medium.
• ATEX or certificate requirements and the destination site in Oman or the GCC.
• Spares you want quoted with the pump, such as seal service kits.

Documents and quotation

We do not host a datasheet for the Twin Screw pump on this page. Send us the pump size or nameplate data and we will confirm which official documents are available for it.

Seven Star LLC is an independent supplier in Muscat and quotes against the information you provide. Please send the list above and we will reply with availability and lead time.