Differences between resilient seated soft sealing gate valve and metal to metal seated hard sealing gate valve

Gate valve,also called sluice valve, water gate valve, is one kind of switching device used in industrial pipelines to connect and shut off the medium flow. Gate valves can only be fully opened and fully closed, and can not be used as a regulating and throttling device. 

With different stem structure, gate valve can be divided into rising stem gate valve(also known as OS&Y gate valve) and non rising stem gate valve. 

With different standards, there are DIN gate valves, ANSI AWWA gate valves, JIS gate valves, BS 5163 gate valves, API gate valves. 

With different body materials, there are gray cast iron gate valves, ductile iron gate valves, carbon steel WCB gate valves, stainless steel gate valves, copper alloy gate valves. 

With different sealing materials used, gate valve can be divided into resilient seated soft sealing gate valve(like EPDM lined soft sealing gate valves, PTFE seated soft sealing gate valves) and metal to metal seated hard sealing gate valves, while with different sealing material used, gate valves can be used for different pressures and temperatures. 

Today we are going to discuss the differences between soft sealing gate valves and metal hard sealing gate valves: 

In short, the soft sealing structure refers to the sealing between metal material and non metallic material, like EPDM/PTFE. While the metal hard sealing structure refers to the sealing between metal material and metal material. 

Soft sealing gate valve and metal hard sealing gate valve are for the sealing material of the valve seat. The sealing surface on the valve body of the hard sealing gate valve is precision machined with the body material to ensure the matching accuracy with the valve plate, generally, the welded materials are copper or stainless steel. The soft sealing structure of the soft sealing gate valve means that the sealing material lined on the valve seat is a non metallic material. Because the soft sealing material has a certain elasticity, the processing accuracy requirements for soft sealing structure will be lower than that of the hard sealing structure. 

The differences between resilient seated soft sealing gate valve and metal to metal seated hard sealing gate valve

1. the sealing material difference between soft sealing gate valve and hard sealing gate valve

Soft sealing gate valve and hard sealing gate valve have different sealing materials, the sealing material of soft sealing gate valves are mainly EPDM or PTFE, while the sealing material of hard sealing gate valves are metal material, like copper alloy or stainless steel. 

1.1. sealing structure for soft sealing gate valve:

for soft sealing gate valve, one side of the sealing pair is made of metal material, and the other side is made of elastic non metallic material, that kind of sealing structure is called soft sealing structure. This kind of soft sealing structure has better sealing performance, but that soft sealing structure is not resistant to high temperature, easy to wear and has poor mechanical properties, the soft sealing structure of resilient seated soft sealing gate valve includes steel material+rubber, steel material+PTFE; those soft sealing gate valves are usually used for water pipelines with temperature under 100℃. 

1.2. sealing structure for metal hard sealing gate valve:

for metal hard sealed gate valve, the two sides of it sealing pair are made of metal materials or other hard materials, this kind of sealing structure is called “hard sealing”. the metal hard sealing structure of the hard sealing gate valve has poor sealing performance, but it is high temperature resistant, wear resistant, and has good mechanical properties. The hard sealing structure includes steel +steel, steel+copper, steel+graphite, steel+alloy steel;(those steel material mentioned above may be the cast iron material, cast steel, alloy steel, may also welded and sprayed alloy). Those metal to metal hard sealing gate valves can be used for mediums like steam, gas, oil and water. 

2. resilient seated soft sealing gate valve and metal hard sealing gate valve have different manufacturing process. 

The operating environment of machinery industry is complex, many of which are super low temperature, and low pressure, the resistance of medium is large, and the corrosiveness is strong. Now with the development of valve technologies, metal hard sealing gate valves has been widely implemented. 

Considering the hardness connection between metals, in fact, the hard seal gate valve is same as the soft sealed gate valve, just because it is the sealing between metals. The valve body is required to be hardened, and the valve plate and the valve seat must be continuously ground to achieve great sealing effect. The production period of metal hard sealing gate valve is longer. 

3. soft sealing gate valves and hard sealing gate valve can be used for different conditions. 

Soft sealing gate valves can not be used for high temperature conditions, it will leak under high temperature, while the hard sealing gate valves are suitable for high temperature conditions. Hard sealing gate valve can also be used for high pressure conditions. But the soft sealing gate valves can not be used for high pressure conditions. 

Soft sealing gate valves can not be used for some corrosive mediums, while hard sealing gate valves can be used for corrosive mediums, sometimes the pressure can be 32Mpa or 2500LB. 

For soft sealing gate valve and hard sealing gate valve, which one is perfect? It depends on the mediums, working temperature and pressure. If the medium contains solid particles or can wear the sealing surface, or its temperature is higher than 200℃, it is better to select the hard sealing gate valves, like the high temperature steam, its temperature is generally 180-350℃, under that condition, the hard sealing gate valves should be used. 

4. the soft sealing gate valve and hard sealing gate valve have different cost. 

If the gate valves have the same diameter, pressure grade, and same materials, the cost of hard sealing gate valve is higher than that of the soft sealing gate valve. If for some working condition, both soft sealing gate valve and hard sealing gate valve can be used, considering the limit budget, it is economical to select the soft sealing gate valves. 

5. soft seal gate valve and hard sealing gate valve have some difference in life service period. 

The soft sealing gate valve means its one side of the sealing pair is made of relatively low hardness. Generally speaking, the soft sealing valve seat is made of non metallic materials with certain strength, hardness and temperature resistance, the soft sealing gate valve has good sealing performance and can achieve zero leakage. But the lifespan of soft sealing gate valve is short and its adaptability to temperature is relatively poor. The sealing surface of hard sealing gate valve is made of metal material, its sealing performance is relatively poor. 

The advantage of soft sealing gate valve is good sealing performance, its disadvantage is that it is easy aging and wear, and has short service life. The hard sealing gate valve has a long service life, while its sealing performance is poor. These two kinds of sealing gate valve can complement each other. 

Soft sealing gate valve can not be used for some corrosive materials, while the hard sealing gate valve can solve that problem. 

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