Valve dynamic seal, mainly refers to the stem seal. Do not let the valve with the valve stem movement and leakage of the medium, is the central subject of the valve dynamic seal.

the basic form of stuffing box is:

(1)Cpressed: This is the most used form.

(2)Compression nut type: this form, small size, but the pressing force is limited, only used in small valves.

The filler has the following requirements:

(1)Good sealing;

(2)Corrosion resistance;

(3)Friction coefficient is small;

(4)Adapt to medium temperature and pressure.

Commonly used fillers are:

(1)Asbestos packing: Asbestos packing has good temperature resistance and corrosion resistance, but when used alone, the sealing effect is not good, so it is always impregnated or additional materials. Oil-impregnated asbestos packing: There are two basic structural forms, one is twisted and the other is braided. It can be divided into round and square.

(2)PTFE braided packing: the PTFE thin band woven packing, has excellent corrosion resistance, but also can be used for cryogenic media.

(3)RubberORing: in the low pressure state, the sealing effect is good. The use temperature is limited, such as natural rubber can only be used60C.

(4)Plastic molding filler: generally made of three pieces, can also be made into other shapes.

In addition, the use of units according to their own needs, often explore a variety of effective filler forms.

Bellows seal

With the rapid development of the chemical industry and the atomic energy industry, flammable, explosive, toxic and radioactive substances increased, the valve seal has more stringent requirements, some occasions have been unable to use packing seal, resulting in a new form of sealing-Bellows seal. This seal does not need packing, so it is also called no packing seal.

The two ends of the bellows are welded to other parts. When the valve stem is raised and lowered, the bellows retractable, as long as the bellows itself does not leak, the medium cannot be released. For the sake of insurance, the double seal of bellows and packing is often used.

Static seal

A static seal generally refers to a seal between two stationary surfaces. Sealing method is mainly the use of gaskets.

Washer Material

(1)Non-metallic materials: such as paper, hemp, cowhide, asbestos products, plastic, rubber, etc.

Paper, linen, cowhide and the like, with fine pores, easy to penetrate, when used to be impregnated with oil, wax or other impermeable materials. General valves are rarely used.

Asbestos products, asbestos belt, rope, board and asbestos rubber sheet, etc. Among them, the asbestos rubber sheet has a compact structure, good pressure resistance and good temperature resistance. It is widely used in the valve itself and the flange connection between the valve and the pipe.

Plastic products, have good corrosion resistance, the use of more common. Varieties of polyethylene, polypropylene, soft polyvinyl chloride, polytetrafluoroethylene, nylon66Nylon1010Wait.

Rubber products, soft texture, all kinds of rubber have a certain acid, alkali, oil, sea water resistance. Varieties include natural rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, isobutyl rubber, polyurethane rubber, fluorine rubber, etc.

(2)Metal materials: Generally speaking, metal materials have high strength and strong temperature resistance. But lead is not so, only take its resistance to dilute sulfuric acid characteristics. Commonly used varieties are brass, copper, aluminum, low carbon steel, stainless steel, Monel alloy, silver, nickel and so on.

(3)Composite material: e.g. metal sheath(internal asbestos)Gaskets, combined wave washers, wound washers, etc.

Common gasket performance

When using the valve, often according to the specific situation, replace the original with gasket. There are often washers: rubber flat washers, rubberOShapes, plastic flat washers, PTFE-coated washers, asbestos rubber washers, metal flat washers, metal shaped washers, metal wrapping washers, wave washers, wound washers, etc.

(1)Rubber flat washer: easy to deform, easy to compress, but the pressure and temperature resistance are poor, only for low pressure, low temperature place. Natural rubber has a certain acid and alkali resistance, the use temperature should not exceed60℃;Neoprene is also resistant to certain acids and alkalis, using temperature80℃;Nitrile rubber oil resistant, available80℃;Fluorine rubber corrosion resistance is very good, temperature resistance is also stronger than the general rubber, can be in150Use in the medium.

(2)RubberOShaped washer: The cross-sectional shape is a perfect circle, with a certain self-tightening effect, the sealing effect is better than the flat washer, and the pressing force is smaller.

(3)Plastic flat washer: The biggest feature of plastic is good corrosion resistance,Most of the plastic temperature resistance performance is not good. PTFE for the crown of plastic, not only excellent corrosion resistance, and temperature range is relatively wide, can be in-180℃ ~ 200Long-term use.

(4)PTFE coated gasket: In order to give full play to the advantages of PTFE, while making up for its poor elasticity of the shortcomings, made of PTFE coated rubber or asbestos rubber gasket. In this way, it is not only as corrosion-resistant as PTFE flat washers, but also has good elasticity, enhances the sealing effect and reduces the pressing force.