German SHW Automotive pump SHW Automotive model SHW Automotive price

SHW Automotive pumps are mechanical devices that meter the delivered liquid. They are commonly used in complete chemical dosing systems and are therefore also called dosing pumps. They are a special type of positive displacement pump designed to meet various strict process requirements, with flow rate steplessly adjustable within the 0-100% range for transporting liquids (especially corrosive liquids).

SHW Automotive pump structure and classification

The pump consists of three main parts: motor, transmission box, and cylinder body. The transmission box components include a cam mechanism, stroke adjustment mechanism, and ratio worm gear mechanism; rotating the adjustment handwheel adjusts the tappet stroke, thereby changing the diaphragm extension distance to achieve flow rate adjustment. The cylinder body components include the pump head, suction valve group, discharge valve group, diaphragm base, etc. Dosing metering pumps can be classified by drive type into motor-driven and solenoid-driven. For motor-driven metering pumps, flow rate adjustment can be achieved by using a variable frequency drive to change the motor speed, or by adjusting the piston stroke. Installing a servo motor (ATE) allows left/right rotation to adjust the angle, increasing or decreasing the piston stroke. Solenoid-driven flow rate adjustment changes the diaphragm reciprocating frequency; it can accept pulse frequency from a flow meter or an analog signal of 4～20mA, or accept analog 4～20mA signals from water quality instruments, with the controller regulating dosing. Flow rate can be adjusted manually via buttons, or the dosing amount can be controlled by a controller (PID).

SHW Automotive pump working principle

The motor drives the worm shaft via a coupling, and the worm gear reduces speed to rotate the main shaft and eccentric wheel. The eccentric wheel drives the tappet to reciprocate within the guide tube. Together with the diaphragm, the action of the check valves gradually creates a vacuum in the pump chamber, opening the suction valve to draw in liquid; when the diaphragm moves to the forward dead center, the suction valve closes, the discharge valve opens, and the liquid is expelled by the diaphragm. The pump forms a continuous, pressurized, quantitative discharge of liquid through reciprocating motion with a regulated stroke. Pump flow rate adjustment is achieved by rotating the adjustment handwheel, which turns the adjustment screw, thereby changing the distance between tappets and altering the diaphragm stroke within the pump chamber to determine the flow rate. The handwheel scale determines the diaphragm stroke, with an accuracy of 95%.

SHW Automotive pump precautions

1) What important matters should be noted when operating a dosing system? Injection point pressure, stroke frequency, suction lift height, altitude, and chemical corrosivity. 2) When the metering pump outlet is at atmospheric pressure, what methods can improve the pump's repeatable metering accuracy? Installing a valve spring on the metering pump discharge valve can improve repeatable metering accuracy, but the most effective improvement method is to install a backpressure valve at the end of the pipeline. 3) How to adjust the backpressure valve? When there is pressure at the suction end of the metering pump, the pressure at the discharge end must be at least 1bar higher than the suction end pressure. Never exceed the maximum working pressure of the metering pump. 4) If the transported liquid is not water, how is the suction lift height calculated? Divide the rated suction lift height of the metering pump by the specific gravity of the metered liquid. 5) How to set the safety valve pressure? The safety valve pressure can be adjusted within the rated working pressure range of the metering pump and must not exceed the maximum working pressure of the metering pump. The safety valve is designed to prevent overpressure operation of the metering pump. For example, if the maximum working pressure of the metering pump is 3bar, the safety valve pressure should be set to 3bar, or lower, to ensure normal operation of the metering pump. Overpressure operation is one of the main causes of metering pump damage. 6) How to select the appropriate pulse dampener volume? Multiply the metering capacity per stroke of the metering pump (ml) by 26 to obtain the minimum volume (ml) of the pulse dampener required to reduce pulsation by 90%. 7) Under what circumstances is flooded suction used? When the metered liquid is volatile; when the metered liquid has a high specific gravity; when a high stroke frequency is required; when the metering pump operates at high altitudes; or when field applications require large storage tanks and self-priming by the metering pump is not feasible. 8) Can you provide some recommendations regarding metering pump head selection? What problems usually arise concerning chemical corrosion of the pump head/seals, and how can they be avoided? Problems with metering pump heads typically occur when metering acids, chlorine, fluorides, and hydrogen peroxide. Due to differences in chemical concentration and operating temperature, it is difficult to determine the specific pump head material. When metering fluorides, we recommend choosing a Viton sealed PVC pump head. For most chlorination applications, it is best to choose an EPDM sealed NP (plexiglass) pump head. For metering hydrogen peroxide mixtures, only a PTFE sealed PTFE pump head or stainless steel pump head can be selected. For metering concentrated hydrochloric acid, a Viton sealed plexiglass pump head is usually chosen. For metering concentrated sulfuric acid, a PTFE sealed PTFE pump head can be selected. Chemical manufacturers will provide relevant recommendations, or consult the ProMinent chemical resistance chart to determine compatibility between chemicals and contact materials. 9) What influencing factors must be considered when metering liquid with the pump head? The main factors to consider are liquid viscosity, specific gravity, vapor pressure, and temperature.

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