A rotary valve, also known as a rotary-motion valve, rotary airlocks, or rotary feeders, controls the flow of liquid or gas through the connected pipes by rotating one or more passageways in a transverse plug. The function of rotary valve is to meter the flow of granular bulk or powders. With small pressure loss, material enters the valve by a hopper or other inlets, processed by the valve rotor, and then deposited in discrete packets onto a conveyor system.
Purpose of Rotary Valves
The major purposes of rotary valves are:
- To offer an airlock (pressure seal) between two processes that are next to each other
- To provide solids metering (feeding)
- To provide a pressure seal and solids metering combined for feeding solids into a pneumatic conveying system.
Rotary valves have a wide range of uses in the chemical and food, pharmaceutical, plastic, and other production industries. They can transport items that are dry to slightly sticky.
Operating Mechanism of Rotary Valves
There are four basic parts of rotary valves, which are outer housing, rotor, rotor bearing and seal, and the drive.
The outer housing provides the inlet and outlet ports as well as a safe passageway for material via the valve. The rotor bearing secures the rotor in place. The shaft seal and bearing seal off the material inside the valve inner housing. Driving mechanism controls the rotational speed of rotor and its direction, which is commonly an electric motor, which is mounted on the rotor shaft from the outside. Materials enter the valve, collected into equal pockets between the rotor vanes, and then discharged at the outlets in an equitable distribution. These rotor vanes have a small gap between them and the housing, which keeps material and pressure losses from passing through the valve and maintaining pressure differentials.
Types of Rotary Valve
The rotary valve is available in a wide variety, each best suited for a certain use. Each component may be set up to accommodate various requirements.
Rotary valves are generally manufactured in the following three types:
- Drop-through type
- Off-set or side-entry type
- Blow-through type
In a drop-through valve, the solids input and output are typically the same size and are vertically in line. Solids that flow vertically downward from a hopper above the valve fill the empty rotor pockets as soon as the rotor begins to rotate. The inlets and outputs of these valves can be square, rectangular, or circular; the square design is more popular because it offers a larger opening area than a round opening.
The solids inlet of a side-entry valve is 30 degrees off from the vertical solids-gravity-flow line. Due to this offset, when the rotor turns past the valve intake, the upcoming empty rotor pocket can only fill partially. The solid particles that occasionally become caught between the rotor and the valve housing are less likely to be sheared because to this partial filling. Additionally, partial filling avoids solid particles that may occasionally become caught between the rotor and the valve housing from jamming or seizing the rotor. The empty pocket’s volumetric fill efficiency varies depending on the solid’s flow characteristics, although it is typically about 60%. The inlet section of these valves should include an adjustable slide plate to enable for adjusting the amount of pocket filling.
In contrast to drop-through valves, blow-through valves are inserted directly in the conveying line without the use of an intermediary equipment. In this arrangement, the solids are transported to the opposite end of the rotary valve and directly into the conveying line by the conveying gas, which enters the rotary valve from one end and blows through the emptying rotor pocket. These valves are used for sticky materials that are difficult to remove from the rotor pocket.
The selection of rotary valves will depend on several parameters. Those are:
- Application and performance requirements
- Operating speed
- Rated temperature and rated pressure
- Types of connection
- Material of construction
Application and Performance Requirements
We need to understand the purpose of using rotary valves and their tasks. These include estimating desired throughput rate, specify material properties, such as density and flow coefficient, estimating efficiency, and other important parameters.
Speed of rotor will influence throughput rate, valve wear, valve size, and many aspects. A maximum rotor speed is 40 meters per minute. However, this depends on the type of rotor, the properties of the material, and other factors.
Rated Temperature and Rated Pressure
It is necessary to ensure that rotary valves are sized in accordance with its pressure condition; whether they are used in pressure condition or vacuum condition. To ensure that no component of the valve is stressed, make sure to define the operating temperatures of the environment and the material. The rotor typically expands at a different pace from the housing, which results in considerable thermal effects that might lead to unintended leakage or maintenance (particularly at full speeds). Make sure the rotary valve you choose can withstand the heat and will not exhibit these impacts in your application.
Types of Connection
How will the valve feed and discharge and how will it connect to your bigger system crucial since different feeding and discharge devices can be utilized with varying degrees of success. By mentioning these details, you will be able to locate a rotary valve that has the proper connection features for your application.
Material of Construction
Choose a material that can withstand these stresses after determining the potential chemical and physical interactions between your material and valve. For instance, bronze rotor tips will last longer than other types and stainless-steel rotor blades will resist corrosion from moist media. Material of construction should anticipate lifespan of your project and select a valve material that will maintain pressure/vacuum integrity if necessary.