SUBJECT : Understanding Split Mechanical Seals 3-8

The split seal is the one seal that every consumer wanted. The main reason that people continue to use packing is that no one wants to take the pump apart just to fix a leak. Taking a pump apart involves several problems:

The following illustration shows a modern split seal mounted between the face of the stuffing box and the bearing case. Note that the seal is an extension of the stuffing box and is not installed in a typical "outside seal" configuration. In other words, as the seal faces wear they move away from the solids in the product and not into them. You'll also note that the elastomer always moves to a clean surface, as the faces wear. This is a very important feature if there are solids in the sealing fluid.

The first successful split seals were used on the atomic submarine main propeller shafts back in 1954. They proved to be as reliable as solid seals, but they were very expensive because of a lack of good technology for cutting the lapped faces or joining the O-ring seals. There are three accepted methods of joining the split elastomer components:

Gluing O-rings, or any other type of elastomer together is never acceptable for a dynamic elastomer. The glue creates a "hard spot" that'll prevent proper sealing.

Early split designs were cut in half by "cut off saws" and re-machined to concentricity. This involved a lot of handling and hand finishing operations that added to the original high cost. Today we use lasers, high pressure water tools, fracturing techniques and other types of sophisticated machinery to accomplish the same thing at much lower costs. The fact is that reliable split seals are just about the same price today as any balanced, O-ring, cartridge seal made out of the same materials. Spare part kits are considerably cheaper than comparable solid seal spare parts.

Depending upon the brand and size of split seal that you select, the temperature, speed and pressure limits are just about the same as any other balanced O-ring mechanical seal. The major difference comes in the sealing of vacuum. Some splits seals need a positive pressure to hold the faces together, so if you intend to use the seals in vacuum service, this type must be turned around sputting atmospheric pressure on the sealing side. Stationary split seal do not experience this problem.

The market for split seals is the same as for other mechanical seals, but they also have several markets open to them that other seals cannot satisfy. As an example:

Split seals are the easiest way to convert any packed pump to a mechanical seal. You should convert packed pumps for any of the following reasons:

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