Screw Pump components
Bearings, drive units, materials, coatings and other details
Screw pumps are generally made of normal mild steel with a special epoxy coating. A suitable coating system will be selected for each specific application. Spaans Babcock can also manufacture screw pumps of all sizes in stainless steel. References are available on request.
Due to the rotation of the screw the water is slightly stowed up to one side of the open trough. To prevent the water from flowing back and to increase the efficiency of the screw, a side profile is mounted at one side of the trough.
Protective Epoxy Coatings
In close cooperation with leading producers of preservative products, Spaans Babcock has developed a range of protective coatings for various applications.
The screw pump is suspended from the upper bearing. This means that almost all the load is hanging from the top! The Spaans Babcock upper bearings therefore are specially designed to take up both the axial force as well as the radial force.The Spaans Babcock standard upper bearings are pedestal mounted because installation and pre-alignment are much easier than with the wall-mounted upper bearings.
The lower bearing of a screw pump is a very important component. Its role is to keep the pump aligned and to maintain the accurate gap between screw and trough. Although it carries only a small portion of the load of a screw pump, it has to do its duty under harsh conditions: submerged in dirty water.Spaans Babcock has developed during the last 50 years a large range of lower bearings; the most used types are shown below:
Spaans Babcock LGO (conventional lower bearing)
The traditional lower bearing is based on a non-rotating stub shaft that is rigidly mounted to the bottom of the inlet and a bronze bush sleeve bearing, mounted to the lower end of the screw pump, that is rotating around the stub shaft to ensure that eventual wear will occur evenly distributed.A very small amount of grease is constantly pumped into the bearing by a grease pump that is installed at the top.
Spaans Babcock ECO (totally enclosed lower bearing)
Spaans Babcock developed in cooperation with SKF the ECO bearing: a totally enclosed lower bearing that is based on roller bearings. This bearing does not need any external lubrication and can be operated without grease pump. The advantages are:
- no grease into the water
- no possibility of human error (nobody can forget to fill up the grease!!)
- no consumption of grease and electricity.
The calculated operational lifetime of this bearing is in excess of 100,000 hours.
Spaans Babcock is the only manufacturer that gives the screw pump and lower bearing maximal protection by using guards / shrouds around the lower bearing. By using this cover the possibility of items such as rags, ropes, cables and other debris wrapping around the bearing will be eliminated.Originally this cover was made of cast iron (and often too heavy to handle) but the new ERGO-guard®, made of strong industrial compound plastic, is not heavier than 25 kg whilst having the same or even better characteristics than cast iron.
To absorb shock-load and torque during startup and operation, a heavy duty flexible coupling is used between the drive shaft of the screw pump and the output shaft of the gearbox. Selection of the type and size of coupling is done by experienced engineers.
Spaans Babcock developed a range of drive unit arrangements for all type of screw pumps and all sizes. Although there are many different arrangements, they all consist at least of:
- motor (mostly electric motors however diesel motors are also possible)
- gearbox (to reduce the speed of the driving motor)
- base plates & support frame
- connection between motor and gearbox (see below)
- safety guards
The drive units come pre-assembled on a steel support frame for easy installation and simple alignment.
The connection of the electric motor and the gearbox can be:
- direct connection
- v-belt connection
The advantage of the direct connection (with a flexible coupling or fluid coupling between motor and gearbox) is that it does not require re-adjustment. The disadvantage is that speed-reduction (= speed of the screw pump) can only be done within the available range of reduction ratios from the gearbox supplier.The advantage of the v-belt connection is that a first reduction can be achieved before entering the gearbox. The actual outgoing screw speed can be exactly matched to the theoretical optimum.