Types and Uses of Valves 

Key point summary: Valves are the "switches" and "controllers" of the pipeline system, controlling the on-off, flow rate, direction and pressure of the medium (water, gas, oil, steam, etc.). Choosing the wrong valve can result in minor leaks or even severe explosions. 

Divided into six categories according to functions 

1. Cutting type (on or off, no adjustment) 

Gate valve 

The most common type of stop valve. The gate plate moves vertically up and down. When fully open, the flow resistance is extremely low, and when fully closed, the seal is excellent. It is suitable for large-diameter pipelines and is used for full opening or full closing. It is not suitable for semi-open regulation - when partially open, the gate plate is subject to erosion and is prone to damage. Typical applications: inlet and outlet pipes of water treatment plants, main pipelines of HVAC systems. 

Ball valve

The sphere rotates 90 degrees to achieve the switch function. It has excellent sealing performance, fast switching speed and a small size. It is one of the most widely used valves at present. It is suitable for situations requiring quick cutoff and can also be used for regulation. Typical scenarios: natural gas pipelines, fire protection systems, and main water valves in households. 

Stop valve (cock) 

The structure is similar to that of a ball valve, but it uses a conical plug for rotation. It is resistant to high temperatures and has good sealing performance, but it is not suitable for large diameters. Typical applications: small steam pipelines, laboratory piping. 

Butterfly valve 

The disc rotates around its central axis, fully opened at 90 degrees. It is small in size, light in weight, and low in cost, and is particularly suitable for large diameters (DN600 and above). It can be used for cutting as well as adjustment. Typical applications: ventilation ducts, cooling water systems, and wastewater treatment. 

II. Adjustment Type (Controlling Flow Volume) 

Stop valve 

The valve disc moves up and down along the center line of the valve seat, changing the flow area. It has high adjustment accuracy and good sealing performance, but the flow resistance is greater than that of a gate valve. It is the most commonly used regulating valve. Typical scenarios: steam pipelines, and process pipelines that require precise control of flow. 

Needle-type valve 

The "miniature version" of a stop valve, with a very thin valve needle, allows for extremely precise flow regulation. Typical applications: instrument piping, laboratory gas lines, hydraulic systems. 

Adjustable ball valve / Adjustable butterfly valve 

By adding electric or pneumatic actuators to ordinary ball valves or butterfly valves, remote automatic regulation of flow can be achieved. Typical applications: HVAC water systems, chemical process control. 

III. Check Valve Type (Allows flow in only one direction) 

Lift type check valve 

The valve disc rises and falls automatically due to its own gravity and the pressure of the medium. It provides a good seal, but can only be installed on horizontal pipelines. Typical application: at the outlet of a water pump, to prevent water from flowing back and damaging the impeller after the pump stops. 

Swing-check valve 

The valve disc rotates around the axis to open, resulting in low resistance. It can be installed in both horizontal and vertical pipelines. Typical applications: large-diameter water supply pipes and drainage pipes. 

Buttress type check valve (double flap) 

The two valve discs are closed by the spring force. It is small in size, light in weight and has a fast response. Typical applications: the outlet of fire pumps and the compressed air pipeline. 

IV. Safety Protection Category (Automatic Protection System) 

Safety valve (pressure relief valve) 

When the system pressure exceeds the set value, it will automatically pop open to release pressure, preventing equipment explosion. It is a mandatory component for boilers and pressure vessels. Typical scenarios: steam boilers, compressors, gas storage tanks. 

Pressure reducing valve (pressure stabilizing valve) 

Reduce the imported high pressure to a stable outlet low pressure. Regardless of how the upstream pressure fluctuates, the downstream pressure remains basically unchanged. Typical scenarios: gas station outlet, water supply for high-rise buildings (after pressure reduction, supplying each floor), laboratory gas source. 

Siphon valve (condensate valve) 

Automatically remove the condensate water from the steam pipeline and prevent steam leakage. Incorrect selection can lead to water hammer or steam waste. Typical scenarios: all steam pipelines - HVAC, food processing, papermaking. Common types include float type, thermal power type, and thermal static type. 

V. Special Medium Categories (for corrosive, highly toxic, and highly clean environments) 

Diaphragm valve 

Separate the medium from the valve body using rubber or plastic diaphragms, with the medium only coming into contact with the diaphragm. It is resistant to strong corrosion and has zero leakage. Typical applications: pharmaceuticals, food, semiconductor ultra-pure water, and strong acid and alkali pipelines. 

Fluorine-coated valve (Teflon-lined valve) 

The inner surface of the valve is lined with polytetrafluoroethylene (PTFE), which is resistant to almost all chemical corrosion. Typical application scenario: harsh chemical corrosion conditions in the chemical industry. 

Electromagnetic valve 

The valve core is driven by an electromagnetic coil to switch, which can be remotely and automatically controlled with a fast response. Typical applications include automatic control systems, fire linkage systems, and irrigation systems. There are two types: normally open type and normally closed type. 

The core logic of the selection valve 

First, I would like to ask three questions: 

First, should we truncate or adjust? For truncation, we choose gate valves, ball valves, and butterfly valves; for adjustment, we choose stop valves and needle valves. 

Secondly, what is the medium? For clean water, cast iron valves will suffice; for steam, cast steel or stainless steel can be used; for highly corrosive substances, fluorine-lined or diaphragm valves can be employed; for food and medicine, stainless steel with hygiene grade can be selected. 

Thirdly, what is the diameter? For small diameters (less than DN50), stop valves and ball valves are preferred; for large diameters (above DN300), butterfly valves and gate valves are preferred. 

One-sentence summary 

Valves are the "entrance and exit points" of pipelines. There are over 3,000 types of valves, but in 90% of daily scenarios, it's just a few types: gate valves and ball valves for cutting off, globe valves for regulation, check valves for preventing backflow, safety valves and pressure reducers for safety, and diaphragm valves and solenoid valves for special media. Choosing a valve is not about choosing the expensive one, but the right one.