A diaphragm pump is a special type of positive displacement pump. It relies on the reciprocating motion of a diaphragm to change the volume of the working chamber, thereby drawing in and discharging liquid.
A pneumatic diaphragm pump mainly consists of two parts: the transmission system and the diaphragm cylinder head. The transmission system is the drive mechanism that moves the diaphragm back and forth. Its transmission methods include mechanical, hydraulic, and pneumatic transmissions, with hydraulic transmission being the most widely used. The working part of the diaphragm pump mainly consists of a crank-connecting rod mechanism, a plunger, a cylinder, a diaphragm, a pump body, an intake valve, and a discharge valve. The drive mechanism, consisting of the crankshaft, connecting rod, plunger, and cylinder, is very similar to that of a reciprocating piston pump.
When the diaphragm pump is working, the crank-connecting rod mechanism, driven by an electric motor, drives the plunger in a reciprocating motion. The plunger's motion is transmitted to the diaphragm through the working fluid (usually oil) in the cylinder, causing the diaphragm to move back and forth.
The cylinder head of a pneumatic diaphragm pump primarily consists of a diaphragm that separates the pumped liquid from the working fluid. When the diaphragm moves towards the drive mechanism, a negative pressure is created inside the pump cylinder, drawing in liquid. When the diaphragm moves to the other side, liquid is discharged. The pumped liquid is separated from the working fluid by the diaphragm within the pump cylinder, contacting only the pump cylinder, suction valve, discharge valve, and the pump's internal side of the diaphragm, without contacting the plunger or sealing devices. This ensures that critical components like the plunger operate entirely within the oil medium, maintaining optimal working condition.
The diaphragm must possess good flexibility and corrosion resistance, typically made of materials such as polytetrafluoroethylene (PTFE) or rubber. The perforated, pot-shaped parts on both sides of the diaphragm are designed to prevent excessive localized deformation of the diaphragm and are generally called diaphragm limiters. Pneumatic diaphragm pumps offer good sealing performance, easily achieving leak-free operation, and can be used to pump corrosive liquids such as acids, alkalis, and salts, as well as high-viscosity liquids.
Each of the two symmetrical working chambers of the pump contains a diaphragm, connected by a central connecting rod. Compressed air enters the air distribution valve through the pump's inlet, and the air distribution mechanism introduces the compressed air into one chamber, pushing the diaphragm within that chamber to move, while gas is discharged from the other chamber. Once the end of the stroke is reached, the air distribution mechanism automatically introduces compressed air into the other working chamber, pushing the diaphragm to move in the opposite direction, thus causing the two diaphragms to reciprocate continuously and synchronously. In the diagram, compressed air enters the air distribution valve, causing the diaphragm to move to the right. The suction force of the chamber draws the medium in through the inlet, pushing the ball valve into the chamber. The ball valve then closes due to the suction. The medium in the chamber is compressed, pushing open the ball valve and flowing out through the outlet, while simultaneously closing the ball valve to prevent flow. This cycle repeats continuously, causing the medium to be continuously drawn in from the inlet and discharged from the outlet.
