1.General situation
Food processing is mainly divided into three main processes, namely incoming materials, semi-finished product processing, and finished products. Each link involves the involvement of pumps to some extent. The requirements for pump types are also different. For example, chocolate processing requires pumps that can transport high viscosity media, wastewater treatment requires pumps that are wear-resistant and corrosion-resistant, and pharmaceutical formulation processing requires pumps with good corrosion resistance. For different product manufacturers, the pump materials required at different stages are also different.
▪ The sanitary pump is mainly used for filling, emptying, batching, and mixing. In addition, it is also used to transport process fluid from device equipment such as membrane filters.
▪ There are two main forms of sanitary pumps: centrifugal and volumetric.
▪ Sanitary pumps have become relatively mature abroad, with manufacturers such as Alfalaval, Bominox, CSF, SPX, Grundfos, etc. There are also many manufacturers producing sanitary pumps in China, such as beer production equipment manufacturers.
2.Some relevant standards
Pumps used in the food, beverage, and pharmaceutical industries must meet different hygiene standards, which specify the structural materials and cleanliness standards of the pumps. Unlike other industrial applications, pumps used in the food and beverage industry must comply with strict hygiene regulations.
▪ The 1.3-A standard has been widely implemented in the United States and has also been recognized internationally.
▪ In Europe, the "Machinery Supply (Safety) Regulations" stipulate safety and hygiene requirements for use in agricultural and food equipment.
▪ The standard for centrifugal sanitary pumps in China is "QBT 1826-2010 Centrifugal Sanitary Pumps".
3.Selection of Sanitary Pump Materials
▪ Commonly used are austenitic stainless steel (316L/304), fluoroplastics, ultra-high molecular weight polyethylene, ceramics, glass lining, and so on. For pumps with high cleanliness materials such as distilled water, the flow components are made of ultra-low carbon austenitic stainless steel.
▪ The materials used for sanitary pumps are different from ordinary materials. Because the materials used in pumps are not only corrosion-resistant, but also need to prevent the leakage of harmful elements/substances and the absorption of media that may deteriorate.
▪ China has formulated special regulations for rubber products. For example, the "Hygienic Standards for Rubber Products Used in Food" and steel pipes also specify standards such as QB2003. The safety evaluation method adopts GB17219-1998 or similar methods.
▪ GB17219 mainly uses the soaking method to determine the content of exudates. The standards for materials are not comprehensive. For example, 316L can usually be used in sanitary pumps, but if the 316L steel plate is not produced according to the requirements of hygiene level, it is completely possible to exude trace harmful elements. Therefore, according to GB16798 "Safety and Health of Food Machinery" and GB12073 "Safety and Health of Dairy Equipment", materials that may rust after welding are not allowed to be commonly used. Stainless steel should be non-toxic and non absorbent. Some manufacturers also adopt FDA and 3A certifications.
4.Design and production of sanitary pumps
There are many types of sanitary pumps, which are determined by the diversity of the media they transport. From clean direct drinking water to milk and jam. These materials are acidic and alkaline. There are both those with good liquidity and those that are difficult to flow.
The main types of sanitary pumps are centrifugal pumps, cam pumps, single screw pumps, and peristaltic pumps. Their design method is largely the same as that of ordinary pumps. However, it is not entirely the same. Here, we mainly use centrifugal pumps as an example to briefly explain the points that need to be noted.
▪ There are no dead corners in the flow. In the food production process, the place where the medium comes into contact with the pump. These media need to be flowing. In ordinary pumps, the mechanical sealing chamber is often a dead angle, and in this case, an open or conical sealing chamber is required.
▪ The surface roughness of the weld seam needs to reach 3.2, and generally the surface should reach 0.8. That is to say, the pump body flow channel and impeller flow channel need to be polished. Ordinary cast parts are difficult to meet this requirement. Therefore, centrifugal sanitary pumps generally adopt a stamped and welded structure. Sometimes, the impeller is open or semi open.
▪ Complies with CIP requirements. Most production filling lines require daily flushing. Rinse off any residue that may deteriorate or produce bacteria. Many use clean water for a certain period of pumping or backwashing. This is related to the previously mentioned no dead corners. During a flushing period, all parts with slower media flow (such as materials in the sealing chamber) should flow out.
▪ Meets COP requirements. This requirement is simple for disassembling the pump (such as extracting the bearing box and rotor components of the rear door pump from the pump body). High pressure flushing water can directly reach the surface that needs to be flushed.
▪ Complies with SIP requirements. In addition to using a sterilization radiation, high-temperature water/steam is also commonly used for online disinfection. The temperature for sterilization is generally above 121 degrees. Sanitary pumps that use steam sterilization need to be able to withstand this high temperature (including sealing). Using high-temperature water (water above 121, which definitely requires a certain pressure to maintain its liquid state) requires the pump to withstand high temperatures and certain pressures.
The production of sanitary pumps not only requires equipment for ordinary stamping pumps, but also advanced welding and polishing equipment.
5.Centrifugal sanitary pump
There are two main types of installation: vertical and horizontal, and they can be divided into single stage and multi-stage based on the number of impellers. Due to its simple structure, low cost, continuous operation, and easy cleaning, centrifugal sanitary pumps are widely used in aseptic processes.
Due to the immersion of the impeller in the medium and the high shear force generated by the high-speed rotation of the impeller, it can affect the shear sensitivity of the conveying medium.
Advantages:
▪ Simple structure, durability, and easy on-site cleaning;
• No overpressure due to closed discharge valve;
• Can be connected in series to increase the pressure head;
▪ It can be connected in parallel to increase flow.
Disadvantages:
▪ Usually does not have the ability to self aspirate (except for self aspirated);
▪ Not suitable for applications with viscosity greater than 500cP;
▪ Not suitable for handling shear sensitive products;
▪ It is not suitable to handle fluids with high gas content;
▪ The head is not constant with the flow rate.
6.Positive displacement sanitary pump
Positive displacement pumps are used in situations where viscosity is too high, centrifugal pumps cannot be used, and where flow adjustment is required. Positive displacement pumps have a self priming function and can handle gas containing media. But all positive displacement pumps require pressure safety devices to avoid damage to the pump and system in the event of outlet closure or blockage.
Advantages:
▪ Simple and compact structure, reliable use, long service life, easy manufacturing, convenient maintenance, and self priming;
▪ The internal meshing gear pump has a constant output and minimal vibration;
▪ It can be transported in both directions;
▪ The flow rate does not vary significantly with viscosity and pressure;
▪ Can transport high viscosity media.
Disadvantages:
▪ Only clean fluid can be transported;
▪ Once the gear is worn, it is difficult to repair;
• Cannot idle;
▪ High machining accuracy requirements;
▪ The gear is subjected to unbalanced radial hydraulic pressure, causing severe bearing wear and limiting the increase in working pressure;
▪ The external gear pump has large flow pulsation, resulting in large system pressure pulsation and high noise;
▪ There may be liquid trapping.
7.Roots type sanitary pump, cam rotor pump
Roots pumps have two rotors, with a double or triple blade shape. The rotors rotate in opposite directions, and there are small gaps between the rotors and between the rotor and the inner wall of the pump casing without contact.
The rotor of the cam pump has impeller blades protruding from the wheel hub. According to the number of blades on each rotor, cam pumps can be divided into single leaf cam pumps and double leaf cam pumps.
Advantages:
▪ It can idle for a short period of time, and the allowed time is determined by the quality of the sealing;
• Able to self aspirate;
▪ Can handle solid suspensions;
▪ Having a relatively good net positive suction head (NPSH);
▪ Can handle fluids with higher viscosity (compared to centrifugal pumps);
▪ It can be transported in both directions.
Disadvantages:
▪ Due to fixed clearance, wear can cause a rapid decrease in pump performance;
▪ There are two shafts and two corresponding sets of shaft seals;
▪ The suction head is low and can only operate at low speeds and low viscosity conditions.
8. Flexible impeller sanitary pump
Flexible pump is a type of rotor pump that belongs to the positive displacement pump. It is named after the flexible rotor blades operate in a flexible manner, and is also known as flexible rotor pump or flexible impeller pump. The earliest design can be traced back more than half a century ago, when it was mainly used to clean the oil and water in the cabins of barges and flush the decks. However, due to its excellent performance and the development of elastomer technology, flexible pumps are increasingly being used in various industrial fields. Flexible pumps not only have the main characteristics of positive displacement pumps, but also are a special type of positive displacement pump. The characteristics of a pulsatile liquid flow, which decreases with the increase of outlet pressure and medium viscosity, are similar to those of a centrifugal pump. In many industrial applications, it is often used as a substitute for centrifugal pumps, solving problems that centrifugal pumps cannot solve (media that cannot be transported or working conditions that cannot be adapted to). The flexible rotor is made of flexible materials, and the pump casing is in an asymmetric form. When the rotor rotates, it deforms, causing the volume of the cavity formed by the blades and the pump casing to change and transport the medium.
Advantages:
▪ Able to self aspirate;
▪ Low pressure vibration during liquid pumping;
• Can be transported in both directions;
▪ Can transport gas containing media and suspensions;
▪ Easy to clean.
Disadvantages:
▪ Applicable only to low pressure conditions;
▪ Not suitable for handling fluids with abrasive wear characteristics.
9. Screw sanitary pump
The screw pump relies on the volume change of the working space (working chamber) formed by the meshing of the screw and screw (or screw and liner) to transport liquid.
Advantages:
▪ Capable of self priming;
▪ Stable discharge and low vibration;
• Can be transported in both directions;
▪ Can handle gas-containing liquids;
▪ Can handle suspensions;
▪ Wide viscosity range of conveying medium;
▪ Strong resistance to abrasive wear;
▪ It can handle shear sensitive fluids well.
Disadvantages:
• Cannot idle;
▪ Pump performance is sensitive to viscosity changes;
▪ High processing and assembly requirements.
10. Peristaltic sanitary pump
Advantages:
▪ The medium only comes into contact with the hose and is not contaminated;
▪ Capable of handling gas-containing fluids;
▪ Can transport shear sensitive and oxidation corrosion sensitive media;
▪ Strong resistance to abrasive wear;
▪ Allow the diameter of the solid contained in the fluid to reach 40% of the inner diameter of the tubular element;
• No need for sealing and valve fittings;
▪ High precision;
▪ Capable of self priming;
• Capable of idling;
▪ Having the ability to transport equal flow in both directions;
▪ No damage will be caused to any component of the pump when there is no liquid idling;
▪ Can generate up to 98% vacuum;
▪ Only the hose is a component that needs to be replaced, making the replacement operation extremely simple.
Disadvantages:
▪ Due to the use of flexible pipes, the pressure bearing capacity is limited;
▪ Failure of the conveying pipe can cause product loss;
▪ Low pump speed;
▪ During operation, there will be pulse flow and significant vibration;
▪ The flow range is relatively narrow.