High performance sealing systems for critical pumps
2 Apr 2019
There are various challenges faced by engineers across the world when it comes to high performance sealing systems in critical plunger pump applications, explains Lauren Grice on behalf of FTL Tech.
Plunger pumps are reciprocating pumps suitable for use in high pressure applications of up to 3,000 bar, commonly referred to as ultra high pressure plunger pumps (UHP), high pressure plunger pumps (HP), triplex pumps or quintuplex pumps, depending on application.
Unlike piston pumps, the high-pressure seal is stationary – with a cylindrical plunger pushing through the seal. Pressure within the cylinder chamber actuates the valve at both suction and discharge points.
The challenges
There are various sealing challenges that plunger pump manufacturers can face: location and suction difficulties, delivering low capacity or failing to deliver at all. This is why proper installation and maintenance is so crucial.
Running costs, cross contamination, maintenance, installation errors, downtime, leakage, or seal life present further issues.
Within the crosshead of a plunger pump, some of the most common seal failures occur due to the high speeds of the piston combined with low pressure, the lack of lubrication and high levels of miss alignment putting high demand to the seals. This in turn can lead to costly repairs due to cross contamination to the drive end.
Most engineers will admit that they are not motivated by change unless necessary
Another common area of concern raised by many plunger pump OEMs is the micro leakage of the hydrodynamic film on the piston assembly.
The solution is custom materials and seal profiles to provide controlled contact area, thus reducing running temperatures and wear to the seal. A bespoke seal design can ensure effective self-lubrication without leakage, but it must be easy to install on-site to reduce maintenance costs.
In low-pressure systems, seal friction can raise the required actuating pressure to many times that available in the system. In some special applications where operating pressures are generally lower, it is more difficult to obtain the low friction and high sealing efficiency which are often required.
Low pressure seals can be found between the crosshead and wet end of a plunger pump assembly. With limited space, high running speeds and poor lubrication, low pressure seals are key to isolating coolant systems from leaking to the atmosphere.
With all plunger pumps, it’s essential that the most effective material has been selected, and that careful consideration has been taken on the material finish and geometry of interfacing components to optimise seal design.
Replacing a failed plunger pump is an expensive undertaking, and one of the most common causes of pump failure can be attributed to the seal design and material.
Choosing the correct seals helps ensure longer service life than conventional packings and chevron seal, self-lubricating properties. Cost savings are possible with removal of certain lubrication systems, the right seal can provide reduced low-pressure leakage and be supplied in cartridge form for easy installation.
Furthermore, low friction can result in low power loss, while dry running capabilities, live loading that allows for controlled wear loss, and packing materials suitable for use in abrasive media all provide benefits.
It’s understandable that you’re seeking to use proven products and technology. Most engineers will admit that they are not motivated by change unless necessary, whereby the solution has deteriorated or performed poorly.
However, it’s imperative that you seek expert advice from a professional, experienced engineering company because a solution could be available that would achieve your desired goals.
