Once pump equipment leaks on the production site,many people simply replace the seal without investigating further—under the same working conditions,some mechanical seals can last for years,while others fail within months.The problem often lies in the selection process.A mechanical seal may appear to be just a pair of friction surfaces,but it actually involves multiple dimensions such as material pairing,pressure balance,and structural form.Any parameter deviating from the working conditions may accelerate seal failure.Even for commonly used rotary pumps,improper mechanical seal selection will directly affect operational stability.

-Bonve Pumps Cam-Type Double Rotor Pump-

A mechanical seal achieves sealing through the relative motion of two mating flat surfaces.The rotating face turns with the main shaft,while the stationary face is fixed inside the gland—also known as a dynamic seal.The entire seal assembly has four leakage points:the seal face contact area,the fitting between the rotating face and the main shaft,the junction between the stationary face and the gland,and the connection between the gland and the stuffing box.The latter two fall under static sealing and can be resolved with gaskets or O-rings;what truly determines service life is the dynamic sealing face.In earlier designs,the secondary seal moved axially with the shaft,easily wearing grooves into it.The new generation adopts a stationary design,fundamentally eliminating shaft wear and corrosion.During normal operation,medium pressure presses the seal faces together,while spring force compensates for pressure during startup and shutdown.

The vast majority of mechanical seals use a"soft-on-hard"combination:the rotating face is made of carbon graphite,and the stationary face uses ceramic,tungsten carbide,or silicon carbide.Regardless of the pairing,a liquid film must be maintained between the contact surfaces for lubrication.Excessive pressure squeezes out the liquid film,leading to dry friction and overheating;insufficient pressure widens the gap and causes leakage.The flatness of the seal end faces directly affects performance,requiring specialized lapping processing.Handle with care during installation and align strictly—any bump or deviation may damage the sealing surfaces.

Main shaft operation involves axial float and radial runout,and the seal must have the ability to follow these movements.Traditional single springs have strong initial force but uneven pressure distribution;multi-spring structures provide more uniform force,better anti-clogging capability,and the springs are often isolated from the medium.Under highly corrosive conditions,metal bellows seals are more suitable.Constructed from multiple layers of welded metal discs,they eliminate the need for secondary seals,removing the risk of shaft sleeve corrosion.

The net pressure on the seal end faces is determined by the medium pressure and the effective cross-sectional area,which relates to the selection between balanced and unbalanced types.Unbalanced seals have higher specific pressure and reliable sealing,but generate significant heat,resulting in very short service life under high-temperature and high-wear conditions.Balanced seals reduce the pressurized area through a stepped shaft,lowering end face specific pressure to reduce heat generation and extend service life—however,the specific pressure must not approach zero,otherwise the seal may become unstable or even blow open.When stuffing box pressure exceeds 50 psi,balanced seals are preferred.

In terms of installation form,internally mounted seals are installed inside the stuffing box,offering easy hygiene control but requiring pump disassembly for maintenance.Externally mounted seals are installed outside the gland,featuring simple installation,low cost,convenient monitoring and cleaning,and proximity to bearings with less influence from shaft deflection.The drawback is that centrifugal force throws particles toward the seal face,making them only suitable for clean,abrasive-free media.Cartridge-type split seals can be replaced without disassembling the pump,but the root cause of failure still needs to be identified.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

Service Hotline: 0574-87588986 13586591794  

Official Website: www.bvpumps.com  

Business Email: market@bonvepumps.com  

We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.