The endplates of the rotary valve must be precision machined. It is on the valve’s endplates that the bearings are placed. The endplates are also known as side covers. The main function of the bearings in a system is to facilitate the rotation of the valve’s rotor. The bearings’ setup on the housing endplates can be configured in two distinct ways namely, inboard bearing endplates and outboard bearing endplates. The design of the housing endplates is solely dependent on the aforementioned configuration. During the valve’s assembly the bearings and the seals are directly connected to the endplates.
This is a descriptive configuration of how the bearings are positioned on the endplates. Slightly protruded endplates are used for this configuration and are sometimes considered as flat endplates. If the bearings are directly positioned on the housing endplates, the bearings setup is known as inboard, hence the name inboard bearings. This setup provides greater risks such as contaminating the bearings which may lead to premature breakdown when the seal fails.
In this configuration, the bearings are not directly positioned on the valve's endplates, instead they are situated farther out on the endplates in comparison to inboard bearings. This configuration uses more protruded side covers, there is a gap between the seals and bearings. This configuration offers lesser risks compared to inboard configuration. In the case where a seal fails, the bearings are not compromised. The setup offers lesser chances for a combustible dust stream to be ignited if ever the bearings overheats. The other advantage of this setup is that if high temperatures are involved, the bearings are not easily affected.
The sealed-for-life deep groove ball type bearings are some of the most commonly used bearings in rotary valves. Grease filled bearings that are sealed using neoprene or similar seals are appropriate for temperatures up to 300℃ for high temperature applications. The bearings’ temperature capability can be improved by the use of different materials and lubricants. Generally, the size of the bearings may be associated with the size of the rotor shaft. In other words, their size is dependent on the rotor shaft size. The bearings are susceptible to product contamination. Outboard bearings and inboard bearings are the two distinct configurations applied to a rotary valve’s endplates.
A variety of sealing options with different properties are available to operate in different conditions. A seal is fitted inside the stuffing box situated on the end plates. It prevents the material outflow from the rotor pockets into the bearing region. It also prevents impurities from entering the rotor housing. Failure of the seal compromises the rotary valve system. When compromised, the bearings are put at risk and if combustible materials are processed, the entire valve system becomes dangerous because of the increased risk for material buildup and ignition. Some of the commonly used seals include; gland packing and lip seals. The operating environment affects the lifespan of these seals.
Whenever a gland packing seal is utilized, a gland follower is commonly used to compress the packing. The seal is manually inserted into the stuffing box. It is the most commonly used seal even though it is not necessarily easy to replace. Multiple rows can be depending on the valve model. When several rows are used, they are stacked together to prevent leakages in most valve systems. The seal is made from a mixture of different materials.
The lip seal uses a similar working approach to that of a gland packing seal. The primary function of a lip seal is simply to keep away contaminants and retain lubricants. It also confines pressure. The nature of the seal is to function by maintaining proper contact with the rotating counterpart. The sealing edge diameter is slightly lesser than that of the shaft that is to go through it. The sealing lip (front face) is angled at the point of contact with the shaft in order to reduce friction. The garter spring helps maintain the pressure on the shaft.