|technology > storage & transport > pump|
PumpsIn nearly every food manufacturing company raw materials, half products and end products are moved using pumps. Pumps are also being used for dosing.
Important issues when choosing a pump are:
- Which product is being pumped? What is its density, viscosity, saturated pressure? What are the chemical, grinding and lubrication properties? How about presence of solids?
- What is the plant curve and the NPSH? NPSH = Net Pressure Suction Head; minimum pressure needed at the entrance of the pump to 1) prevent cavitation of a (low viscous) fluid and 2) keep feed of the pump.
- What are the properties of the pump?
Not all pumps are already commercially available in hygienic models, but often other types of pumps can be used.
As a start an ordering has been made based on operating principle: positive displacement or centrifugal.
Positive displacement: a portion of fluid is sucked in and discharged. Possibly pulsating flow.
- GEAR PUMP: between the teeth of two gear wheels little units of fluid are being pumped. The low rpm version is well suited for viscous products. Pumps with high rpm can be used for thin flowing products but not for watery solutions. There are also versions with internal gearing.
- LOBE PUMP: a positive pump. Per rotation a certain volume is being pumped. The pressure is relatively low. Applicable both for low and high viscous flow, even when the fluid contains solid particles.
- VANE PUMP: In an eccentric rotor slots are placed containing movable vanes. By springs or centrifugal force these vanes are pressed against the rotor housing. Due to rotation chambers are formed sucking in and pumping fluid. Not applicable for flows containing solids. Wear particles can also contaminate the flow. A pump with ellipse shaped rotor holding only one vane is suitable for products with high viscosity.
- FLEXIBLE VANE PUMP: Operating like the above mentioned vane pump. But in order to prevent holding of material in the slots of the vanes and thus reduce chance of contamination flexible vanes can be used. By bending these flexible vanes seal against the rotor housing.
- CIRCUMFERANTIAL PISTON PUMP: two rotors rotate in opposite direction and every rotor has elements that fit each other. At the suction side the rotors rotate apart and suck in fluid, and on the outlet side they move towards each other and discharge.
- HOSE PUMP: a number of rolls moves over a hose containing the fluid thus pumping a certain volume. Since there is no contact with the product there is no contamination. Due to wear the hose is the critical factor.
- MULTIPLE SCREWS PUMP: A screwed spindle drives a non driven screw spindle with fitting thread. Between the two screws fluid is being pumped. If the lubrication function of the fluid is insufficient the dummy screw is mechanically driven. But the more spindle inlets the more difficult it gets to work hygienically safe.
- MONO SCREW PUMP: A screw-shaped rotor moves in a rubber casing (stator). The rotor moves to-and-fro and presses away fluid axially. The rotor is driven by an propeller shaft. This type of pump is excellent for dosing with little pulsation. However is cannot stand running dry and the rubber stator is subject to wear.
- PISTON PUMP: A piston is moving to the lowest point creating low pressure and through inlet valves fluid enters the cylinder. When the piston reaches the highest point the fluid is pumped out through outlet valves. This causes the outlet flow to pulsate. Solutions to minimize this effect: press also on the other side of the piston, apply several piston pumps parallel or add pulsation dampeners.
- PLUNGER PUMP: The same principle as the piston pump with the piston replaced by a plunger: a piston with the same diameter as the piston rod. Suited for small flux and high pressure. Often used as dosing equipment.
- MEMBRANE PUMP: Comparable to the piston pump but with a membrane in stead of a piston. This membrane can be driven by motor, by air or by oil. In principle this pump can function hygienically, it has no problems with running dry and it can be used to dose. The quality of the membrane determines the durability of the pump.
- SINE PUMP: Using a sine-shaped rotor 4 chambers are filled and emptied, causing hardly any pulsation. A scraper drives the product out and prevents reflux to the suction side. It is a mild way of pumping. Slip is possible along the rotor. Compare an eccentric disc pump.
Centrifugal: Fluid is being hurled outwards and in the centre low pressure is created which sucks in fluid.
- CENTRIFUGAL PUMP: Pressure building pump. If the pump sucks in air it cannot pump any more. This type of pump is very well suited for pumping thin viscous fluids. It is called “sanitary centrifugal pump” in the food manufacturing industry.
- MULTI-STAGE CENTRIFUGAL PUMP: A centrifugal pump with several impellers for building up higher pressure. This can be achieved by placing impellers in one casing or by placing several single stage pumps in series.
- SELF PRIMING CENTRIFUGAL PUMP: Using extra appliances this centrifugal pump is capable of pumping air if the pressure drop is limited. It is always necessary to have liquid available at starting up.
- JET PUMP: Following the Venturi-principle a jet of fluid creates low pressure and powder, liquid or gas can be sucked into the jet.