Driver screw

This is the part of a twin screw pump used to help the pump transfer consistent flow at any instant of rotation. This screw rotates together with the driven screw with close clearance to transfer the fluid forward along the axis of rotation. This screw is a spindle with screws machined on it and made of a strong material such as high tensile steel. The driver screw is tasked to rotate the driven screw by the use of a timing gear. As the driver screw gently moves along the low clearance together with the driven screw to help produce low shear effect. This also helps to enhance the life of the pump as it avoids conditions such as fluid medium emulsification in case of contaminated water or impacting negatively on the other machinery connected to the pump.

Driven screw

The driven screw is made of the same strong material as the driver screw such as high tensile steel. This screw gets power from the timing gear. The driven screw in a twin screw pump rotates in opposite direction to the driver screw. The driven screw has consistent clearance which helps to catch fluid into the tight clearance. As the driven and driver screws rotate together, fluid volume decreases and it moves to the outlet port. The fluid pressure increases due to this movement. Finally, the fluid exits the pump via the outlet port.

Timing gear

As both the driver and driven screw run with fine clearance they could by chance make contact. A single contact can easily wear the screw edge thus drastically reducing output pressure. If it is not checked, it can easily make the twin screw pump far less efficient and uneconomical as well as make the screws lock each other. As such, a timing gear is used to check such cases. The timing gear is used to drive the driven screw such that there is no metal-to-metal contact between the driver screw and the driven screw. Also, this gear ensures zero metal-to-metal contact of the screws in case the pump runs dry for a certain period.

Suction and discharge port

Twin screw pumps have various inlet and outlet ports as the fluid being pumped moves along the screw axis of rotation to the discharge port. The inlet and outlet ports are made in a way that helps them to hold enough fluid when the pump turns off. This provides initial fluid into the pump and thus it prevents the pump from running dry for a short period even when the suction pipe is dry or empty. The inlet port gets partial vacuum when there is a pressure difference between the pump inlet and discharge port. This creates the energy needed to transfer the fluid into various confined areas in the screw clearance. As the inlet port experiences partial vacuum, the outlet port experiences high pressure where the pump tries to push more fluid.

Pressure relief valve

The twin screw pump can build up pressure while its outlet is closed. This pressure can result in damage to the internal parts of the pump or even cause injury to the pump operator. As such, twin screw pump manufacturers design the pump with a relief valve. This valve helps to protect the operator and pump and other connected machinery. The use of this valve is to send back excess pressure to the inlet section.

Bearings

In a twin screw pump that is vertically mounted the bearings that experience higher loads are those on the upper side. These bearings experience radial and axial forces when the pump is working. This makes the bearings on the lower side experience very low loads. The lower bearings are meant for sustaining the alignment of parts in the pump. For twin screw pumps installed in parallel, the sliding and roller bearings used experience very low loads. This happens because the axial and radial forces on the bearings are in opposite directions thus canceling out their magnitudes.

Driving shaft

The driving shaft on the twin screw pump is used to connect the motor shaft to the other parts of the pump. The connection is attained by the use of a flexible coupling. In twin screw pumps, the driving shaft is sometimes used as a key part that runs from each side to secure the rotation of the drive screw. In such designs, the driving shaft uses bearings fitting in the axial direction. This makes the alignment of the driving shaft very important as its slight misalignment can make the pump malfunction.

Stationary and rotary seal

Twin screw pump manufacturers design the pumps with mechanical seals to seal the surface between the working fluid and the dry side of the pump. This helps to keep the timing gear and the bearings separated on one side of the twin screw pump as the shaft coupling and the bearings separate on the other side. Other twin screw pumps have extra gland packing mounted after the mechanical seal to enhance leakage-free seal at the suction. It is recommended that if a mechanical seal leaks 6 to 8 drops in one hour be replaced immediately with a new one. This is because as it remains unchecked the leakage grows quicker and quicker and it may damage the pump.