There are soft and hard seals on the sealing faces in valves, so what is the difference between the two?

First, the structural mechanism

Hard seal valve is a seal between metal and metal, the sealing surface and valve seat are metal, the processing accuracy and process are more difficult, generally used in high pressure, usually more than 2.5MPa. Soft seals are seals between metals and non-metals, such as nylonPTFE, and the manufacturing standards are the same.

Second, the sealing material

The soft and hard seal is the sealing material of the valve seat, and the hard seal is precision machined with the valve seat material to ensure the matching accuracy with the valve core (ball), generally stainless steel and copper. Soft sealing means that the sealing material embedded in the valve seat is a non-metallic material, because the soft sealing material has a certain elasticity, so the processing accuracy requirements will be lower than that of hard sealing.

Third, the manufacturing process

Due to the complex working environment of many chemical and machinery industries, many of them are high temperature and high pressure, the friction resistance of the medium is large, and the corrosiveness is strong.

In fact, the principle of hard seal valve is the same as that of soft seal, but because it is a seal between metals, it is necessary to consider the hardness relationship between metals, as well as working conditions, what medium to go, etc. Generally, it is required to do hardening treatment, and the sealing surface should be continuously ground to achieve sealing. The production cycle of hard seal valves is long, and the processing is more complicated, which is not easy.

Fourth, the conditions of use

Soft seal valves can generally achieve high seals, while hard seal valves can be high or low according to requirements; Soft seals need to be fireproof, because at high temperatures, the material of the soft seal will leak, while the hard seal does not have this problem; Hard seals can generally be made at very high pressures, but soft seals cannot; Due to the problem of the medium flowing, the soft seal cannot be used in some occasions (such as some corrosive media); Finally, hard-seal valves are generally more expensive than soft-sealed. As for the manufacturing, there is not much difference between the two, the main thing is the difference between the valve seats, the soft seal is non-metallic, and the hard seal is metal.

Fifth, in the equipment selection

The selection of soft and hard seal valves is mainly based on the process medium, temperature and pressure, the general medium contains solid particles or has wear or the temperature is higher than 200 degrees, it is best to choose a hard seal, the diameter is greater than 50 valves, the pressure difference of the valve is larger, and the torque of the opening valve should be considered to be large, and the hard seal valve should be selected when the torque is larger.

How to choose between soft and hard sealing areas of valves?

1. Soft sealing

In addition to corrosion-resistant lined valves, general soft-seal valves refer to valves in the form of a seal in which one of the spools or seats is made of non-metallic materials (mainly PTFE, rubber, etc.). The sealing effect of the soft seal valve is the best, but it is possible to leave more or less unclean debris (such as welding slag, iron filings, etc.) in the pipeline installation and system cleaning, and when they flow through the control valve, it is easy to scratch the soft seal seat or valve core, which increases the leakage and poor sealing reliability. Therefore, the selection of soft seal structure must consider the cleaning of the medium and the strict flushing of the pipeline before operation.

2. Hard sealing

Hard seals, resurfacing welding, wear-resistant alloys, etc. are the best choice for shut-off valves. This method also considers the service life and reliability while considering the tightness, although the factory index is only 10-6~10-8, which can not achieve the effect of zero leakage of soft sealing, but it is enough to meet the requirements of tight cutting, and it is durable, and it is more cost-effective from an economic point of view.

(The article comes from the Internet)