Sealing part of valve

The contact between the two sealing faces of the opening and closing parts and the valve seat, the fitting position of the packing with the valve stem and the stuffing box, and the joint between the valve body and the valve cover. One of the former leakage is called internal leakage, which is usually said to be not tight, it will affect the ability of the valve to cut off the medium. For block valves, internal leakage is not allowed. The leakage at the last two places is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve.

Leakage will cause material loss, environmental pollution and even accidents. For flammable and explosive, toxic or radioactive media, leakage is not allowed, so the valve should have reliable sealing performance.

How to solve the sealing problem can not be ignored, valve running, emitting, dripping, leakage phenomenon, as most departments occur here. Next we will discuss the valve dynamic seal, static seal problem.

1. Dynamic seal

Valve dynamic seal, mainly refers to the valve stem seal. It is a subject of valve dynamic sealing to prevent the medium in the valve from leaking with the movement of the valve stem.

1) Form of stuffing box

The main packing box is valve. The basic form of stuffing box is as follows:

(1) Gland type

The unified form can distinguish many details. For example, from the hold down bolt, it can be divided into T-bolt (for pressure ≤ 16 kg / cm2 low-pressure valve), stud bolt and union bolt, etc. From the gland, can be divided into integral type and combined type.

(2) Compression nut type

This type of form, small size, but the compression force is limited, only used in small valves.

2) Filler

In the stuffing box, the packing is directly contacted with the valve stem and is covered with the stuffing box to prevent medium leakage. The following requirements are required for fillers:

(1) Good sealing; (2) corrosion resistance; (3) low friction coefficient; (4) compliance with medium temperature and pressure. Genius valve

2. Static seal

What is static seal called? Static seal usually refers to the seal between two stationary surfaces. The main sealing method is to use gasket.

gasket material 

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

Paper, hemp, cowhide, etc. have pores and are easy to penetrate. When used, they must be impregnated with oil, wax or other impermeable materials. General valves are rarely used.

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

Plastic products have good corrosion resistance and are widely used. Varieties of polyethylene, polypropylene, soft PVC, polytetrafluoroethylene, nylon 66, nylon 1010 and so on.

Rubber products, soft, all kinds of Rubber Division has a certain acid, alkali, oil, sea water resistance. Varieties of natural rubber, styrene butadiene rubber, nitrile rubber, chloroprene rubber, isobutylene rubber, polyurethane rubber, fluororubber and so on.

(2) Metal materials: Generally speaking, metal materials have high strength and high temperature resistance. However, lead is not the case. It is only characterized by its resistance to dilute sulfuric acid. Commonly used varieties are brass, copper, aluminum, low carbon steel, stainless steel, Monel alloy, silver, nickel, etc.

(3) Composite materials: such as metal clad (internal asbestos) gasket, composite corrugated washer, surrounding entangled washer, etc.