In recent years, split seals have become another important additional feature in outer seals. The separate seal is a complete assembly, installed between the stuffing box and the bearing sleeve. With this design, it is not necessary to disassemble the liquid pump every time the seal needs to be replaced. Such seals are being developed in conjunction with other design criteria discussed. Since this design allows for easy seal replacement, it is important to resist the temptation to simply replace the seal without further investigation into the root cause of the failure. The cartridge seal is an all-in-one sealing device, which includes all sealing elements, glands and bushings. Since this type of seal does not require any strict installation measures, the installation procedure is greatly simplified, and the sealing surface and sealing elastomer are well protected to prevent accidental damage. These advantages also mean that seal repair and replacement times are reduced.

Almost all kinds of cartridge seals are available on the market, so the risk factor in use can be reduced, and it can also save the maintenance time inherent in the use of ordinary seals.

Double seal and liquid barrier

The use of double sealing surfaces instead of a single seal has a higher degree of leak-proof characteristics. Most of these double seals are used in highly volatile, toxic, carcinogenic, dangerous and poorly lubricated liquids.

There are generally three design types of double seals, each of which requires a liquid barrier system between the double sealing surfaces to prevent leakage of liquid or gas. The more commonly used low-cost dual seal is a back-to-back mounted seal with rotating sealing faces aligned in opposite directions. It often requires a barrier liquid, whose pressure should be higher than the pressure of the stuffing box, about 20psi, so as to ensure that the internal seal can always be lubricated by the barrier liquid, and also ensure that the sealing surface reaches a certain sealing pressure.

In the face-to-face type seal with relatively complex structure, the rotating sealing surfaces are arranged in a face-to-face manner, and they often move in the opposite direction of the same static sealing surface. These seals are available in both high pressure and low pressure barrier fluid systems.

A third design uses a tandem arrangement of seals, where both rotating seal faces face in the same direction away from the impeller. The barrier liquid pressure of this seal is generally lower than the pressure of the liquid pump. In fact, it is equivalent to two sealed, two-stage pressure-reducing joint working devices.

All types of double seals require barrier fluid systems. They are generally external closed-loop systems, and the liquid used inside is generally different, but must match the liquid in the process. The system includes a reservoir located as close to the seal as possible.

The design of these systems varies widely. Some systems use a pump ring in the seal, while others use the principle of the thermosiphon effect. The liquid in the liquid storage tank often adopts the method of auxiliary heating or auxiliary cooling. In addition, an alarm device can be added to remind the staff to replace the liquid in time.

Depending on the nature of the liquid being sealed, barrier fluid systems can operate at pressures below or above the stuffing box.

In order to achieve the goal of zero leakage during the entire driving operation, the sealing industry has also developed a gas barrier seal, which uses an inert gas such as nitrogen to replace the liquid barrier system. In the double seal with gas barrier, if the inside of the sealing surface fails, only the inert gas will leak, and the liquid inside will not leak, thus will not cause environmental pollution.

Regardless of whether liquid or gas is used, the barrier system must be suitable for the specific sealing application, and once any failure occurs inside the sealing surface, the alarm should be recognized immediately so that appropriate measures can be taken in time.