The quantitative piston pump is a hydraulic pump in which the volume of oil discharged by the pump (i.e. displacement) is fixed when the pump shaft rotates once. The structure is simpler than the variable pump and it is widely used. When the pump shaft rotates once, the volume of oil discharged by the pump (i.e. displacement) can be adjusted with a variable plunger pump.

Features of quantitative plunger pump:

1. The self-designed quantitative pump rotor can provide liquid supply capacity within the range specified by the customer.

2. The unique positive pressure structure makes the melt flow rate more stable.

3. Customized according to customer requirements, and can be matched with various brands and models of die-casting equipment.

Fixed piston pump structure:

The quantitative piston pump is mainly composed of two parts: the power end and the hydraulic end, and is equipped with pulleys, check valves, safety valves, pressure stabilizers, lubrication systems, etc. The specific structure is as follows:

1. Power end

(1) Crankshaft: The crankshaft is one of the key components of this pump. Using the integral type of crankshaft, it will complete the key step of changing from rotational motion to reciprocating linear motion. In order to balance it, each crankshaft pin is 120° from the center.

(2) Connecting rod: The connecting rod transmits the thrust on the plunger to the crankshaft, and converts the rotational motion of the crankshaft into the reciprocating motion of the plunger. The rod section adopts an I-shape, the big end is split type, the bearing bush adopts the form of halved thin-walled tiles, and the small head bushing adopts the bushing type and is positioned accordingly.

(3) Crosshead: The crosshead connects the swinging connecting rod and the reciprocating plunger. It has a guiding role. It is closedly connected to the connecting rod and connected to the plunger clamp.

(4) Floating sleeve: The floating sleeve is fixed on the machine base. On the one hand, it isolates the fuel tank from the sewage pool. On the other hand, it serves as a floating support point for the crosshead guide rod, which can increase the service life of the moving seal components.

(5) Base: The base is a stressed member that installs the power end and connects the liquid end. There are bearing holes on both sides of the rear of the base, and a positioning pin hole connected to the liquid end at the front to confirm the alignment between the center of the slide and the center of the pump head. There is a drain hole on the front side of the base to discharge leaking liquid.

2. Liquid end

(1) Pump head: The pump head is made of stainless steel and is integrally forged. The suction and discharge valves are arranged vertically. The suction hole is on the bottom of the pump head, and the discharge hole is on the side of the pump head. It is connected with the valve cavity, simplifying the discharge pipeline system.

(2) Sealing letter: The sealing letter and the pump head are connected by a flange. The sealing form of the plunger is a rectangular soft packing made of carbon fiber textile, which has good high-pressure sealing performance.

(3) Plunger: The spring in the middle of the guide pillar tightens the head ball for telescopic positioning.

(4) Inlet valve and discharge valve: Inlet and discharge valves and valve seats are low-damping, cone-shaped valve structures suitable for transporting liquids with high viscosity, and have the characteristics of reducing viscosity. The contact surface has high hardness and sealing performance to ensure that the inlet and outlet valves have sufficient service life.

3. Accessory supporting parts

(1) Check valve: The liquid discharged from the pump head flows into the high-pressure pipeline through the low-damping check valve. When the liquid flows in the reverse direction, the check valve closes to dampen the flow of high-pressure liquid back to the pump body.

(2) Pressure stabilizer: The high-pressure pulsating liquid discharged from the pump head changes into a relatively stable high-pressure liquid flow after passing through the pressure stabilizer.

(3) Lubrication system: Mainly the gear oil pump draws oil from the oil tank to lubricate the crankshaft, crosshead and other rotating parts.

(4) Pressure gauge: There are two types of pressure gauges: ordinary pressure gauges and electric contact pressure gauges. Electric contact pressure gauge is an instrument system, which can achieve the purpose of automatic control.

(5) Safety valve: A spring slightly opened safety valve is installed on the discharge pipeline. It can confirm the sealing of the pump at rated working pressure and open automatically when overpressure occurs to provide pressure relief protection.

Working principle of quantitative plunger pump:

The forward and backward movements of the diaphragm are used to cause the change between the diaphragm and the pump head to cause the ball valve to move up and down to form vacuum adsorption and pushing phenomena to achieve the purpose of liquid transportation.

① When the diaphragm is pulled back, the outlet ball valve falls down and tightly fits the ball seat. The inlet ball valve floats upward due to the vacuum generated between the diaphragm and the pump head when the diaphragm is pulled back, and the liquid is sucked up.

② When the diaphragm is pushed forward, the inlet ball valve and the ball seat are airtight so that liquid cannot pass through, while the outlet ball valve is pushed forward by the diaphragm and the liquid is spit out.

The difference between quantitative piston pump and variable piston pump:

Under the condition of constant rotation speed, the variable output flow rate is a variable displacement piston pump, and vice versa is a fixed displacement piston pump. The biggest difference between them is that the shaft of the variable piston pump is installed eccentrically. Simply put, after the fixed speed piston pump is selected, its flow rate cannot be adjusted. The output flow of the variable piston pump can be automatically adjusted according to the pressure change of the system (the size of the external load). That is, the output flow is small when the pressure is high, and the output flow is large when the pressure is low. In this way, it can save the number of hydraulic components, thereby simplifying the oil system and reducing oil heat.