A rotary valve controls the flow of dry powder and other solid granules under gravity and a vacuum condition in a circular motion. Its parts should be precision machined to make sure that they would fit and perform they way it is expected to do and allows to be used in pressurized conditions. Each design is suited only for a particular purpose and not be used for other purposes.
A rotary valve has three functions:
1. Provide an air seal (acts as an airlock for vacuum system). If there is no valve to act as a seal, the vacuum will not be sustained. Usually used for pneumatic systems.
2. Provide product metering (acts as a feeder).The valve discharges a certain product at a given rate.
3. Provide combination of air seal and product metering. Where a gravimetric or volumetric feeder is required in a pneumatic system.
Different designs should be considered with proper study to be able to say that the valve is good and appropriate for the system:
1. Make sure you know the type of materials passing through system. If the material is a type of food, then the whole system must be designed to carry food and no contamination would likely happen. The grease on the bearing must have no contact with the powder to avoid contamination. The design should be strict for food products.
2. Housing - the design should make sure no product accumulation anywhere in the system to avoid clogging and contamination of the products. Housing must be made of cast iron, cast steel, cast aluminum or cast stainless steel.
3. Rotor design should be considered. Proper sizing must be done for the alignment of valve rotor, rotor shaft and bearings. Made of steel or stainless steel.
4. Drive design - must be able to start the valve at full load
5. Bearing Design - should be anti-friction type and must be lubricated before shipment
6. Construction Data - no weld splatter or slag is permitted on interior and exterior surfaces. Must be done by certified welders from ASME code.
7. There should be provision to easily remove rotor and endplates to check if there are product materials retained in the rotary valve.
8. The valve should create only a little noise during operations.
9. The ease of doing maintenance activities is a good sign that the design of the valve is studied very well. This must be put into consideration because this is an integral part of the valve. Once there is difficulty in maintenance then you might disregard doing maintenance for your control valve which in return lowers its life span. Refer to how to maintain a rotary valvefor proper maintenance procedures.
10. Valve spares - make sure of availability of spares for possible breakdowns. These spare units must follow the guide given by the supplier. If you are going to use other supplier for a generic spare part, make sure it complies with similar regulations or standards as the main supplier.