General overview
Food processing is mainly divided into three main processes, namely incoming materials, semi-finished product processing and finished products. Pumps are more or less involved in each link. Among them, the requirements for pump types are also different. For example, chocolate processing requires pumps that can convey high-viscosity media, wastewater treatment requires wear-resistant and corrosion-resistant pumps, pharmaceutical processing requires pumps with good corrosion resistance, etc. For different product manufacturers, the pump materials required at different stages are also different.
Sanitary pumps are mainly used for filling, emptying, ingredients and mixing. In addition, it is also used to transmit process fluids from devices such as membrane filters.
There are two main forms of sanitary pumps: centrifugal and volumetic.
Sanitary pumps are relatively mature abroad. Alfalaval, Bominox, CSF, SPX, Grundfos and so on are produced by such pumps. There are also many manufacturers of sanitary pumps in China, such as manufacturers of beer production equipment.
Some relevant standards
Pumps used in the food, beverage and pharmaceutical industries must meet different hygiene standards, which set out the structural material and cleanliness standards of the pump. Unlike other industrial applications, pumps used in the food and beverage industry must meet strict hygiene regulations.
The 1.3-A standard has been widely implemented in the United States and has also been recognized internationally.
2. In Europe, the "Mechanical Supply (Safety) Specification" stipulates the safety and hygiene requirements for agricultural food equipment.
3. China's centrifugal sanitary pump standard "QBT 1826-2010 centrifugal sanitary pump".
Selection of sanitary pump materials
Commonly used are austenitic stainless steel (316L/304), fluoroplastics, ultra-high molecular weight polyethylene, ceramics, enameled glass, etc. For pumps of high-clean materials (such as distilled water), the flow parts are made of ultra-low-carbon austenitic stainless steel.
The materials used for sanitary pumps are different from ordinary materials. Because the pump material is not only corrosion-resistant, but also does not need to seep harmful elements/substances, nor absorb potentially deteriorated media.
China has formulated special standards for rubber products. For example, the "Hygiene Standards for Food Rubber Products", steel pipes also specify QB2003 and other standards. Its safety evaluation method adopts GB17219-1998 or similar methods.
GB17219 mainly uses the immersion method to determine the content of exudate. The standards for materials are not comprehensive. For example, 316L can usually be used in sanitary pumps, but if the production of 316L steel plates is not produced according to the requirements of the sanitary level, it is completely possible to seep out trace amounts of harmful elements. Therefore, GB16798 "Safety and Hygiene of Food Machinery" and GB12073 "Safety and Hygiene of Dairy Equipment" stipulates that materials that may rust after welding should not be used, and stainless steel should be non-toxic and non-absorbent. Some manufacturers have adopted FDA and 3A certifications.
Design and production of sanitary pumps
There are many types of sanitary pumps, which is determined by the diversity of the medium they convey. From clean direct drinking water to milk and jam. These materials are acidic and alkaline. There are some with good mobility and some with difficult mobility.
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 exactly the same. Here, we mainly take the centrifugal pump as an example to briefly explain the points that need to be paid attention to.
1. There is no dead angle in the flow. In the food production process, the place where the medium comes into contact with the pump. These media need to be fluid. In ordinary pumps, the mechanical sealing cavity is often a dead corner. At this time, an open or conical sealing cavity is required.
2. The surface roughness of the weld needs to reach 3.2, and the general surface should reach 0.8. That is to say, the pump body channel and the blade channel need to be polished. It is difficult for ordinary casting parts to meet this requirement. Therefore, centrifugal sanitary pumps generally adopt a stamping and welding structure. Sometimes, the impeller is open or semi-open.
3. Meet the requirements of CIP. Most production filling lines need to be rinsed once a day. Rinse off the residues that may deteriorate and produce bacteria. Many of them use clean water for pumping or backwashing for a certain period of time. This is related to the no dead angle mentioned earlier. During a flushing period, all parts with slow medium flow (such as materials in the sealed cavity) should flow out.
4. Meet the requirements of COP. This requires simple pump disintegration (such as rear-door pump, bearing housing and rotor parts pulled out of the pump body). High-pressure flushing water can directly reach the surface that needs to be rinsed.
5. Meet the requirements of SIP. In addition to using a sterilized ray for online disinfection, high-temperature water/steam is also commonly used. The sterilization temperature is generally above 121 degrees. The sanitary pump with steam sterilization needs to be able to withstand this high temperature (including sealing). Using high-temperature water (water above 121, it must require a certain pressure to maintain a liquid state) pump needs to withstand high temperature and a certain pressure.
In addition to the equipment of ordinary stamping pumps, the production of sanitary pumps should also have advanced welding and polishing equipment.
Centrifugal sanitary pump
In terms of installation form, there are two categories: vertical and horizontal. According to the number of impellers, it can be divided into two categories: single-stage and multi-stage. Due to the simple structure, low cost, continuous operation and easy cleaning of centrifugal pumps, centrifugal sanitary pumps are widely used in sterile processes.
Because the impeller is immersed in the medium, and the high-speed rotation of the impeller will produce a high shear force, which will affect the shear-sensitive conveying medium.
Advantages:
• Simple structure, durable and easy to clean on site;
• There will be no overpressure due to the closing of the discharge valve;
• It can be connected in series to increase the indump;
• It can be connected in parallel to increase the traffic.
Disadvantages:
• Usually do not have the ability to self-suction (except for self-suction);
• It should not be applied in occasions where the viscosity is greater than 500cP;
• It is not suitable to handle shear-sensitive products;
• It is not suitable for handling fluids with high gas content;
• The lift does not change with the flow rate.
Volume-type sanitary pump
Volumetric pumps are used for occasions where the viscosity is too high, the centrifugal pump cannot be used, and the flow rate needs to be adjusted. The volumetric pump has a self-priming function and can handle gas-containing media. However, all volumetic pumps require pressure safety devices to avoid damage to the pump and system when the outlet is closed or blocked.
Advantages:
• Simple and compact structure, reliable use, long service life, easy to manufacture, convenient maintenance, self-suction;
• The internal meshing gear pump discharge is constant and the vibration is very small;
• It can be transported in both directions;
• The flow rate does not change much with viscosity and pressure;
• It can transport high-viscosity media.
Disadvantages:
• Only clean fluid can be transported;
• Once the gear is worn out, it is difficult to repair;
• Can't be irted;
• High requirements for processing accuracy;
• The gear is under unbalanced radial liquid pressure, the bearing is seriously worn, and the improvement of working pressure is limited;
• The external meshing gear pump has a large pulsation, resulting in a large system pressure pulsation and high noise;
• There will be a trapped liquid phenomenon.
Roots sanitary pump, cam rotor pump
The Roots pump has two rotors. The rotor shape is double-leaf or three-leaf, and the rotor turns opposite. There are small gaps between the rotors and the inner wall of the pump shell without contact with each other.
The rotor of the cam pump has a blade protruding from the hub. According to the number of blades on each rotor, cam pumps are divided into single-bedge cam pumps and double-bed cam pumps.
Advantages:
• It can be irled in a short period of time, and the time allowed is determined by the quality of the seal;
• Can self-inhale;
• It can handle solid suspension;
• It has a good net positive suction inder (NPSH);
• It can handle fluids with higher viscosity (compared with centrifugal pumps);
• It can be transported in both directions.
Disadvantages:
• Due to the fixed gap, wear will cause the performance of the pump to decline rapidly;
• There are two shafts and two sets of corresponding shaft seals;
• The suction range is low and can only operate under low-speed and low-viscosity conditions.
Flexible impeller sanitary pump
Flexible pump is a kind of rotor pump among volume pumps. It is named after the blades of the elastomer rotor to operate in a flexible way. It is also known as flexible rotor pump and flexible impeller pump. The earliest design can be traced back to more than half a century ago, when it was mainly used to clean up oil and water in the cabin of barges and to flush the deck. However, due to its excellent performance and the development of elastomer technology, flexible pumps are increasingly used in various industrial fields. Flexible pump not only has the main characteristics of volume pump, but also is a special volume pump. The characteristics of non-pulsating liquid flow, outlet pressure, medium viscosity increase and flow rate decrease are similar to those of centrifugal pumps. In many industrial applications, it is mostly a substitute for centrifugal pumps, which solves problems that centrifugal pumps cannot solve (media that cannot be transported or working conditions that cannot be adapted). The flexible rotor is made of flexible material, and the pump shell is asymmetrical. When the rotor rotates, the rotor is deformed, so that the cavity volume formed by the blade and the pump shell changes, and the medium is conveyed.
Advantages:
• Can self-inhale;
• The pressure vibration is relatively small when pumping liquid;
• Can be transported in both directions;
• It can transport gas-containing media and suspension;
• Easy to clean.
Disadvantages:
• Only applicable to low-voltage working conditions;
• It is not suitable for handling fluids with abrasive and wear characteristics.
Screw sanitary pump
The screw pump transports liquid by changing the volume of the working space (working cavity) formed by the meshing between the screw and the screw (or the screw and the bushing).
Advantages:
• Self-suction;
• The discharge is stable and the vibration is small;
• Can be transported in both directions;
• Gas-containing liquids can be handled;
• It can handle turbidity;
• The viscosity range of the conveying medium is wide;
• Strong ability to resist wear and wear;
• It can handle shear-sensitive fluids better.
Disadvantages:
• Can't be irted;
• The pump performance is sensitive to viscosity changes;
• High requirements for processing and assembly.
Peristaltic sanitary pump
Advantages:
• The medium is only in contact with the hose, without pollution;
• It can handle gas-containing fluids;
• It can convey shear-sensitive and oxidative corrosion-sensitive media;
• Strong ability to resist wear and wear;
• Allow the solid diameter contained in the fluid to reach 40% of the inner diameter of the tubular element;
• No need for seals and valve fittings;
• High precision;
• Self-suction;
• Can be irted;
• It has the ability of equal flow transmission in both directions;
• It will not cause damage to any part of the pump without liquid operation;
• It can produce a vacuum of up to 98%;
• Only the hose is a part that needs to be replaced, and the replacement operation is extremely simple.
Disadvantages:
• Due to the use of flexible tubes, the pressure is limited;
• Failure of the conveying pipe will cause product loss;
• The pump speed is low;
• When working, it will produce a pulse flow with large vibration;
• The flow range is relatively narrow.