Mechanical seal installation

Figure 32.63 A typical mechanical seal installation. 1 Seal chamber 2 seal plate 3 spring sleeve 4 seat 5 seal ring 6 spring 7 dynamic secondary seal 8 static secondary seal 9 flush connection...

Interna] and External Seals Mechanical seals are classified broadly as internal or external. Internal seals (Fig. 10-112) are installed with all seal components exposed to the fluid sealed. The advantages of this arrangement are (1) the ability to seal against high pressure, since the hydrostatic force is normally in the same direction as the spring force (2) protection of seal parts from external mechanical damage and (3) reduction in the shaft length required. 

Install mechanical seal fluid reservoir low level sensor with alarm... 

Sometimes you hear people say that the pump is operating off its cw. t velocity, the impeller diameter and design are correct, if the pump installed and functioning correctly, including the mechanical seal and impossible to operate off the curve. The pump will be somewhere on between shut-off head and maximum flow a zero elevation. 

High Pressure - Installed with baek-up rings, o-rings arc the standard in high pressure mechanical sealing. 

Cartridge mechanical seals are designed so that the rotary and stationary elements, the springs and secondary seals, the gland, sleeve and all accompanying parts are in one integral unit. It installs in one piece instead of the numerous individual pieces. 

The storeroom techs must protect the mechanical seals handling them with extreme care. The engineer or technician must specify and select the seal components correctly. The mechanical maintenance technician must protect the seal at the moment of installation. Once the seal is installed into the pump, the seal requires the correct environmental controls to assure optimum life. At this point the work of the maintenattce technician ends. 

Most seal companies provide a set of instructions and engineering schematic with each mechanical seal to help the mechanic determine the correct installation dimension. These instructions assume ... 

For most applications, the balanced, o-ring cartridge seal will adequately handle every pump, liquid, and condition in a modern industrial process plant. There are, however, some industrial pumping applications that will present problems to even the best of mechanical seals. Should one of these applications cause the seal to give less than desirable performance, the next step to take in extending the service life of the seal (and ultimately the pump) is to install some type of environmental control to protect and isolate the seal components from the fluid. Let s consider some difficult sealing applications. 

MODIFIED STUFFING BOX. .. available with Jahn Crane Type I mechanical tealt. These mechanical seals are easy ta install in the field and are carried in stack. 

Figure 3-18 illustrates a seal installed in a conventional stuffing box with cooling liquid flow path. Figures 3-18, 3-19A, 3-19B, 3-20 and 3-21 identify the fundamentals of mechanical seals, even though there are many specific designs and details. These various designs are attempts to correct operational problems or seal weaknesses when... 

Mechanical seals, which are typically installed in applications where no leakage can be tolerated, are described and discussed in this section. Toxic chemicals and other hazardous materials are primary examples of applications where mechanical seals are used. 

However, much more precision and attention to detail must be given to the installation of mechanical seals compared to conventional packing. Nevertheless, it is not unusual for mechanical seals to remain in service for many thousands of operational hours if they have been properly installed and maintained. 

This section describes the installation procedures for packed stuffing boxes and mechanical seals. 

A mechanical seal s performance depends on the operating condition of the equipment where it is installed. Therefore, inspection of the equipment before seal installation can potentially prevent seal failure and reduce overall maintenance expenses. 

Install a dial indicator with the stem against the shoulder of the shaft. Use a soft hammer or mallet to lightly tap the shaft on one end and then on the other. Total indicated end play should be between 0.001 and 0.004 inches. A mechanical seal cannot work properly with a large amount of end play or lateral movement. If the hydraulic condition changes (as frequently happens), the shaft could float, resulting in sealing problems. Minimum end play is a desirable condition for the following reasons ... 

Mechanical seals are often chosen and designed to operate with environmental controls. If this is the case, check the seal assembly drawing or equipment drawing to ensure that all environmental control piping is properly installed. Before equipment startup, all cooling and heating lines should be operating and remain so for at least a short period after equipment shutdown. 

When starting equipment with mechanical seals, make sure the seal faces are immersed in liquid from the beginning so they will not be damaged from dry operation. The following recommendations for seal startup apply to most types of seal installations and will improve seal life if followed ... 

Maximum Allowable Working Pressure, code, 399, 405, 406, 408 Mechanical seals, 171-177 Fundamentals, 172 Inside, 172 Installations, 173 Lubrication, 174 Outside, 173 Seal flush system, 176 Tandem, 177... 

Unlike a packed gland, a mechanical seal, when correctly installed and maintained, can be considered leak-tight. 

Mechanical seals and glands for all pnmps, except vertically suspended pumps shipped without drivers moimted, shall be installed in the pnmp before shipment and shall be clean and ready for initial service. On pnmps whose seals reqnire final adjustment or installation in the field, the vendor shall attach a metal tag warning of this reqnirement. 

When mechanical seals and drivers are not installed prior to shipment, the seal piping system shall not be fully assembled. 

To protect the HPRT outlet casing integrity and mechanical seals from possible downstream back pressure transients a relief valve installed in the HPRT outlet piping circuit should be considered (see Figure C.1). 

Installing mechanical seals, permanent packing, and accessories in rotating equipment. 

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