Chemical delivery needs are growing. Over the years, non-leaking magnetic centrifugal pumps have been widely used in chemical plants. As environmental regulations become more stringent and application requirements become more demanding, leak-free pump manufacturers must provide reliable and durable pumps. Daniel Roll of Finish Thompson tells about the company's latest technological advances. Leak-free magnetic centrifugal pumps are a type of chemical delivery pump. In order to make them work better, pump users are in urgent need of self-priming pumps that are self-priming and have a robust construction with reliable sealing elements made of engineered thermoplastic for a wide range of applications Chemicals. Many industries that use chemicals often import and export chemicals to storage tanks, tankers and other containers. Due to the increasing emphasis on environmental issues, the trend now is to deliver from the top of the container rather than the sides or bottom, thereby reducing the chance of chemicals leaking through the wall components. This is an ideal application for self-priming centrifugal pumps. Such pumps require rapid self-priming and respiration, and are capable of handling many high specific gravity chemicals. Pump and inlet must be sealed to prevent self-absorption delay or loss of self-absorption. Therefore, the pump's sealing element needs to be very durable. As with other pumps, self-priming pumps must be easy to install, operate and maintain. The new self-priming pump features a compact, leak-free magnetic drive structure and fast self-priming time. Finish Thompson's SP Series pumps are made of thermoplastic material with snap fasteners for internal components and have a "gooseneck" shape in the suction tube. These details constitute the excellent self-priming and running characteristics required for corrosive material delivery, durable static sealing and space-saving structural design. Figure 1. The SP Series self-priming pump uses four standard O-ring seals that are extremely reliable and durable. The SP Series self-priming pumps are sealed with four durable and reliable standard O-rings. A large O-ring (3/16 "cross-section diameter) is also used on the DB Series non-self-priming pump with end face / axial seal with fixing force provided by housing bolts. A smaller radial O-ring seals the water inlet of the pump housing water outlet. The O-ring is sealed radially with a convex sealing sleeve. There are also two O-rings with a cross-section of 3/32 inch in diameter, one for the water inlet and one for the water outlet. They are also designed to be radial and screwed with drain and fill plugs. All O-ring seals are static and O-rings are completely contained in their glands. Sealing in a self-priming pump is important because minimal gas leakage may prevent or delay self-priming. The "gooseneck" shape of the water inlet allows the standard o-ring to be used in any sealing position in any size and shape. The water inlet pipe connects and carries fluid from the suction nozzle in the pump housing to the inlet of the impeller. The "gooseneck" makes a difference between the height of the suction nozzle and the center line of the impeller, so that the resuspended fluid can be retained in the pump housing. When the pump is turned off, the fluid in the suction tube returns to the source and siphons the fluid in the pump housing and drain. Eventually, the height deviation caused by the suction tube will destroy the siphon, the liquid will be trapped in the pump housing and will be used to re-suck the pump when the pump is started again. Designers can use a complex model with a telescopic core as part of the pump housing to simulate the inlet pipe. Instead of using this simulation technique in other designs, the centerline height difference of the self-priming was obtained by making the pump housing in two parts and by complex sealing and fixing. Simulating the SP pump housing as a whole also makes the size of the pump compact, neither too long nor too high. The SP Series is the only one-piece, pump-casing thermoplastic pump with gooseneck-shaped tubing and incorporates a leak-free magnetic drive design. Pump suction and discharge pipe nozzle seal maintenance is also important. Air leaks on the suction line pipe connections can adversely affect the self-priming function of the pump. Therefore, the type and construction of existing connectors are carefully considered and the standard connectors are NPT threads and BSP threads. The secondary seal was made on the BSP pump housing and the joints (made of polyethylene and PVDF) were also secondary sealed with O-ring face seals and flanges. The fittings and flanges are all welded and sealed to the pump housing. The flange includes a moistened thermoplastic convex portion and a separate backing ring of composite or steel material to provide strength and rigidity to the flange bolts. Flange gasket meets ANSI 150 and ISO PN40 specifications. They are not fixed, can be rotated to any location is very easy to install. Pump Start To pump the pump to create a vacuum, a liquid ring is created around the impeller inlet in the inner volute. The volute has a lower port, which connects to the reservoir in front of the pump housing to replenish the self-priming liquid in the liquid ring. The outlet of the volute lies in the upper half and the high velocity mixture of liquid and gas exits there and circulates around the inner volute. Eventually, the fluid flows toward the high speed part of the pump housing through a separating plate into the larger volume of the pump housing where the fluid velocity decreases. At lower velocities, the gas separates from the priming liquid, exits the pump housing and enters the sewer system. The liquid ring can lift water up to 25 feet (at normal atmospheric pressure) and can lift up to about 15 feet in 90 seconds. Figure 2 is SP11 and SP15 two sizes of self-priming pump height and self-priming time diagram. Figure 2. SP Series pump start-up time, including both polarities of 50 Hz and 60 Hz. The inner volute is mounted on the front of the bulkhead and has three spring-loaded snap fasteners. The snap-on bars are integrally formed with the bulkhead, using either 40% glass-filled polypropylene or 15% carbon-filled PVDF. This design avoids the use of metal or other fasteners without compromising the corrosion resistance of pump materials. SP series self-priming pump focused on the overall performance improvement, with DB series end-suction pump similar design. All hardware is metric and accommodates a wide range of NEMA and IEC motor structures. In addition, the SP Series pump has taken a number of steps to give the pump similar performance at 50 Hz and 60 Hz. To achieve this goal, the impeller and the inner volute are machined to larger diameters. At 50 Hz and 60 Hz, the pump performance will not be exactly the same, but very close. Therefore, you can usually use the same pump size to indicate a certain level, regardless of the frequency of the AC motor. This is especially beneficial for OEMs that sell their products in the global marketplace. There are subtle differences between the plumbing and start-up procedures for a standard (non-self priming) end suction centrifugal pump and a self-priming centrifugal pump (such as an SP Series pump). The suction line should be short, hermetically sealed and contain an elbow, either large or small, with sufficient (but not excessive) immersion depth. Too much suction (larger than the pump inlet diameter) will lead to a longer start-up time than normal start-up. For standard suction side suction pump suction pipe, the installation location should not be high. If possible, the pipe should be tilted up to the pump. The purpose is not to prevent "air resistance," but to avoid loss of flow rate that can be caused by air resistance in the suction tube. The design of the outlet pipe also affects the performance of the self-priming centrifugal pump. Self-priming centrifugal pump starts, must provide some space for gas to leave the suction port, discharge from the outlet. There are several ways to provide this space. The first is to open the outlet pipe, including opening the control valve (if used) during start-up and pump self-priming. Once the water flow is formed, the valve can be adjusted to control the proper flow rate. If the check valve is installed in the outlet, or if the control valve does not open at power on, the check valve and control valve must be located downstream of the pump so that there is enough space to discharge the sucked air. It is a good idea to place the first valve somewhere at least a bit downstream of the ascent height. If the valve must be placed near the pump and can not be opened, the air must pass through the pump outlet into the atmosphere or back to the suction source. Figure 3. SP Series Pumps Handling Spilled Ferric Chlorides Widely Used in a Recycling Plant This pump uses a leak-free magnetic coupling torque transmitter that contains a rare earth neodymium magnet. This robust coupling makes it possible to use standard motors with full voltage start-up. This coupling also applies to liquids with a specific gravity above 1.8. SP series pumps can be used in areas with a large number of chemicals such as underground storage tanks, truck unloading, sump and plating tank. These pumps have been used for drinking water sampling, mine dehydration and pH adjustment, electroplating and cleaning programs, and wastewater treatment.
