As a former mechanical engineering student of the then RTC, now Cork Institute of Technology (CIT), I always had an interest in pumps and process engineering. I recently gave a talk on pump fundamentals in University College Dublin for an event hosted by Engineers Ireland.
At the event, I spoke about pump sizing and 'like children, there are no bad pumps - just pumps in the wrong environment'. One example would be where pumps were sized based on 'future expansion' and therefore oversized and a VSD solution could put the pump running at below a minimum Hz.
When selecting a centrifugal pump, it is all about BEP (best efficiency point) and noting the net positive suction requirement of the pump compared to the net positive suction available in a system. But, be careful, the system changes. I gave examples of pumping highly viscous fluids and using the Pumpsmart VSD to its full potential through analogue inputs and outputs to protect the pump.
Many VSDs never used to their full potential
Many VSDs are never used to their full potential and are used only to pass on a signal to speed up or slow down. Pumpsmart has sensor-less protection which is very beneficial to protecting your magdrive pumps from dry running. It is also important to note the weakest component of a centrifugal pump - the seal.
If a seal is being replaced regularly on a pump, then the application needs attention and design input to ensure the correct pump is being used. Sometimes it is not a good idea to replace a damaged pump with the same pump. Ask the questions, why did it fail?
What was the mean time between failures? What was actually happening when it failed? Remember, three per cent of entrained air can reduce the performance of a pump by up to 50 per cent.
When you look at the total ownership of a pump, you will find it should cost anywhere between five and 10 per cent initially (capital investment), and then come the maintenance and power costs during the lifetime of the pump, the figures should be 30 per cent and 45 per cent respectively. Selecting the right pump is very important to reduce costs incurred on maintenance and power.
Selecting the correct pump can lead to an increase in product yield
In some cases, selecting the correct pump can lead to an increase in product yield by the pump being more gentle to the product going through it. This resonates with me when thinking of a recent case study where a Discflo pump was significantly more successful for an application on pumping crystals compared with the standard centrifugal pump.
The crystals were protected in the transfer process and the pump paid for itself in one week with the increased production yield. However, if the focus had been on initial cost, the customer may not have considered the Discflo pump solution.
The effects of specific gravity and viscosity on pumps can also alter your pump selection and result in a decision to select a positive displacement pump. The system friction curve will always play an important role in deciding where your pump is operating on the curve. In some cases, there may not be an option to change pipework.
Open to receive support from the pump suppliers
Installation guidelines from the operator’s manuals occasionally do not get communicated all the way to construction. It is important that end users are open to receive support from the pump suppliers during pump selection and also attend the site to review the possible installation.
Your pump supplier may see opportunities to show savings on the project or can be used on existing installs to suggest modifications. We often see case studies from customers to say the “simple change of increasing the impeller to full size and retrofitting a VSD has saved us approximately €50,000 on just one pump” and “changing the size of cooling and heating pumps in a central utility building without VSDs has saved €200,000 a year”.
As a parting comment: always review the pumps that are running 24/7, 48 weeks of the year. 1kW saving here could equate to €850. If you ask the maintenance department “where are the bad actors with regard to pumps or valves”, they will know.
Author: Eoin Field, business development manager, ESI Ultrapure