Have you ever wondered why the impellers on your industrial pump have holes in them? Some impellers even have vanes on the backside. The short answer to why your impeller has holes or vanes is to reduce the axial thrust in the pump.
For the long answer, check out this week’s blog post from Sintech, India’s leading and most trusted industrial pump manufacturer and exporter.
Regardless of your centrifugal pump’s size or design, the dynamic forces generated in the pump have to be managed properly for trouble-free pump operation. A centrifugal pump that is efficiently designed will address all these forces, thereby eliminating the effects of these forces in play. Of all the dynamic forces in a centrifugal pump, the two main ones to consider are:
Axial forces and
Radial forces
Axial forces act on the rotor in a direction parallel to the centreline of the shaft. On the other hand, radial forces work at a right angle to the centreline of the shaft. In this post, let’s take a look at the impact of axial forces on the pump.
Why do axial forces occur in the pump?
Axial forces arise due to variations in pressure between one side of the impeller and the other. The high pressure acting on one side creates an axial force. The main area on which the axial force acts is the impeller shroud.
How are axial forces negated by impeller design?
The axial force can be neutralised by using balance drums in large multistage pumps. Few multistage pumps also use opposite impellers to counteract the effect of axial forces. For instance, in a six-stage centrifugal pump, 3 impellers face in one direction. In contrast, the other 3 are positioned in the opposite direction.
Another example of negating the impact of axial forces is by using an impeller with two inlet eyes positioned 180-degrees from each other. In this case, the two holes balance out the axial force and negate its impact.
99% of end-suction pumps use semi-open impellers. These impellers have a shroud on one end. The design of these impellers makes them less expensive and easy to manufacture. However, one drawback using impellers with shrouds is that there is a chance of higher unbalanced axial forces. Under general operating conditions, the force on the impeller’s back is much higher than the forces on the front. As a result, the forces try to push the impeller towards the suction end. Due to the axial forces’ effect, suction pumps can experience up to 850 pounds of pressure towards the suction end.
You can reduce the impact of these forces by installing bigger thrust bearings. However, the downside of this move is that bigger bearings require bigger shafts and housings, all of which increase the pump’s initial price and maintenance costs.
This is where balance holes in the impeller come into the picture. By using the right number of holes in the impeller, the axial force can be negated. The one minor drawback of impeller holes is that they reduce pump efficiency and power. However, the reduction in pump efficiency is so minimal that it doesn’t matter in the long run.
The Bottom Line
Every part of your pump is meticulously designed after hours of research by the engineering team. Even something as small as holes on the impeller play a crucial role in ensuring pump operational efficiency without any troubles for years to come.
For the best range of industrial pumps in India, drop in a line to our friendly sales team at sales@sintechpumps.com. Our team will analyse your requirements and help you find the best pumps for your needs.