A mechanical seal helps join systems together in pumps, valves and pipes whilst preventing leaks. Even though they are often a small component within a larger system they are still crucial in ensuring the effective running of many hydraulic systems.
This is especially critical within the assembly of Slurry Pumps which usually transfer abrasive, semi-solid materials which can include anything from cement to starch to manure. Within Centrifugal Slurry Pumps, a shaft is inserted into the pump in order to drive the impeller. This drive shaft is immersed in the material which is being pumped and as such a shaft seal is required to avoid leakage.
A mechanical seal consists of two parts, one that is fixed to the stationary pump housing and the other which is ‘pushed up’ against the shaft using a spring loaded fixing. This allows a tiny amount of fluid, called the Fluid Film to flow between the minute space between the two surfaces. This creates a seal and also serves to provide lubrication and cooling. Getting the Fluid Film right can have a big impact in the part life of the seal. If the film is too thick it will increase leakage and may allow the materials between the faces, if it is too small then this may generate heat and degrade materials. No matter what the application however, this lubricating film at the sealing interface is always needed.
Proper flushing plans will help keep abrasive material away from seal faces as well as serving the purpose of preventing building up within the pump, most noticeably in the stuffing box where stagnation/build-up is most likely to occur. As a general rule of thumb you should also try and avoid dry running conditions as well.
Poor equipment conditions which can be caused by bad bearings, cavitation and misaligned shafts will cause vibration and shock to the seal and there will also be more opportunity for abrasive material to enter the sealing faces causing failures.
Heavy Slurry contains a high solid content and so will have the cause the most wear damage on the component. Selecting the right material is crucial. Most Mechanical seals will be constructed out stainless steels, or high chromium alloys in order to provide maximum hardness. The seal faces themselves will often be thermally sprayed with Tungsten Carbide Coating, further adding to wear and corrosion resistance.
B&B Precision offer full machining and coating of mechanical seals and have a lot of experience in the valve, pump and hydraulic industries. Send us a drawing today and see manufacture your sealing components.