How MIP technology makes pumping so much easier
The development of the maintain in place pump design revolutionises the maintenance requirements of PC pumps – and reduces the burden of maintenance on wastewater treatment works and other facilities, says Simon Lambert.
Widely known for their ability to easily and efficiently transfer a number of difficult media, the performance of progressing cavity (PC) pumps can have a considerable bearing on how energy and cost efficient a treatment works is, as well as its quality of discharge.
However, even with the use of screens and grinders, PC pumps can still suffer from ragging and maintenance issues. Coupled with new problems facing the industry such as diminishing in-house expertise and unsuitable items finding their way into the sewers, difficult processes are becoming even more of a challenge.
A recent survey to discover the common problems facing the wastewater industry found that ragging has become a serious problem and is increasing in severity to the point where it could cause serious disruptions to the efficiency of the treatment process.
While PC pumps can cope with low levels of rag much better than most other types of pump, higher concentrations will undoubtedly cause blockages. The survey revealed that the current options available to engineers when de-ragging a pump were limited, time consuming and in some cases unsafe.
It was clear that the industry needed a pump solution to minimise plant downtime and maintenance, and provide a safer and easier option for today's plant engineer. In response, a new generation of PC pump has emerged that has been designed to provide a quick and easy way to disassemble, de-rag and maintain a PC pump in-situ, eliminating the costly maintenance and down time that servicing can often cause.
On average, this new type of maintain in place (MIP) pump can reduce the maintenance time needed to replace a rotor, stator, coupling rod and joint by up to 95%. The average time to strip down and replace the drive train elements is usually one full day on typical sludge pumps; with this new MIP pump it takes just 30 minutes. Blockages can occur in the suction or inlet chamber of a PC pump. Here, a rotating shaft can become entangled with pieces of rag (or indeed any other fibrous material).
While intervals between maintenance on a PC pump are typically long depending on the application, its design means that access to the suction chamber during maintenance requires dismantling of the pump and pipework connections, in order to get at the chamber. However, when the suction chamber is blocked, especially with fibrous material wrapped around the rotating shaft, the material has to be removed. Blockage of the inlet can rapidly cause damage to the rotor, stator and drive train, so it is imperative that it is caught in time.
Frequently, the problem is only noticed when the flow stops and the protective electrical relays are tripped out; this signifies major downtime.
If detected in time, the maintenance engineer frequently tries to free-up the suction chamber by removing the rag elements with as little of the pump dismantled as possible. This can be a
temptation to adopt dangerous practices, such as inserting a sharp blade through the inlet flange and hacking away at the wound-on and compacted rag, then trying to retrieve the pieces.
The alternative has been to dismantle the pump, which requires unbolting the inlet and delivery flanges and possibly removing a section of pipework to give the necessary dismantling space. Next is the removal of the stator element, which also requires space, especially in the bigger pumps, to withdraw it along the length of the rotor - as much as 50% of the length of the pump needs to be left free to allow this.
Then, the rotor needs to be uncoupled and the suction chamber in some cases will need to be removed from the drive train, depending on the extent of the ragging. The drivetrain may also require attention and the electrical connections must be isolated for such extensive work.
Even by a highly experienced maintenance engineer, this process can take up to a day and the actual cleaning out portion is only a fraction of the time taken to complete a maintenance procedure.
By completely rethinking the design of the suction chamber and drive train element of a PC pump, it is possible to eliminate the difficulty, time and cost of de-ragging and maintenance.
The chamber of the MIP pump has a two-piece design, which can be dismantled and assembled in place without requiring years of expertise. It can be opened up and rebuilt with a spanner and an Allen key in a fraction of the time previously required; timed on-site trials have indicated that it can save up to 95% of the time normally required to provide full maintenance for a PC pump.
The coupling rod can be accessed in less than one minute, the suction chamber and rotating parts de-ragged and the chamber reassembled; the whole operation taking less than two and a half minutes, depending on the severity of the blockage.
For a full MIP procedure, all rotating parts can be removed and replaced in under three and a half minutes, allowing the pump to be completely maintained in situ. The drivetrain can be dispatched as an assembled unit, so on-site assembly by a skilled engineer is not required.
The suction and discharge pipework can be left connected, minimising any pressure testing requirements, and reducing the danger of possible leakage. In installations where space is at a premium, eliminating the requirement for the stator dismantling space can be a great bonus. There is also no need to disrupt electrical connections and access to the whole pump is easy and safe.
Proving that this revolutionary technology can change the way in which treatment works operate, Southern Water installed six EZstrip MIP pumps from NOV Mono at its Sludge Treatment Centre (STC) in Millbrook following a trial to test out claims that it could be de-ragged in 2½ minutes and fully stripped down and maintained in just 30 minutes.
After seeing the performance benefits of this EZstrip pump, Southern replaced its remaining pumps, which included models from another PC pump manufacturer, with five more EZstrip pumps. They have been installed to transfer sludges at different stages in the process, including centrifuge feed, digester feed and cake dilution.
Similarly, two of Mono's EZstrip PC pumps have also been installed at Thames Water's Bicester sewage treatment works to improve process efficiency by reducing maintenance downtime. The development of the MIP pump design revolutionises the maintenance requirements of any PC pump and will reduce the burden of maintenance on not just wastewater treatment works, but all facilities that use PC pumps.
Simon Lambert is general manager, Europe, for NOV Mono. www.mono-pumps.com