Rotary valves are a vital part of any pneumatic conveying system, so keeping them running efficiently is important for industries involved in bulk material handling. Air purge kits are often used to help optimize the operations of a rotary valve. Seal purge kits – the most commonly used purge kits for rotary valves – do this by protecting the seal from contamination during operations that involve higher internal pressures or when processing extremely fine powders. While there are other methods of purging a rotary valve, seal purge kits are the most effective, and their use within a system helps keep other components operational.  Such purging helps remove material buildup around the shaft seal, helping prevent the premature wear of a rotary valve. Seal purge kits help lengthen the valve's life, so understanding how they work will help operators keep their material processing systems up and running.

What is a Seal Purge Kit and How Does it Work?

With a rotary valve, seal purge kits keep waste products and other impurities from contaminating seals. Depending on the application, rotary valves are used as either feeders through which product is conveyed and/or as airlocks to maintain a differential pressure between the valve’s internal components and the external production environment. This is particularly important when operating under conditions that place higher internal pressures on the rotary valve. Seal purge kits are accessories used to prevent this pressure, which can cause product to find the path of least resistance, to escape through the rotary valve seal. Purging the valve helps prevent this from happening.

For a rotary valve, seal purge kits generally operate like this:

  1. Air or an inert gas – like argon or nitrogen – is typically used as a purging medium, which is introduced into the inboard of the shaft seals.
  2. This purging medium flushes the area in front of the seal, creating a higher pressure zone than that within the valve.
  3. Careful control is exerted over the purge kit so as not to interfere with the valve’s normal operation.

Seal purge kits help keep a system running optimally by preventing contaminants from impeding the functions of material handling equipment while also optimizing processing efficiency and augmenting product quality. To understand which type of purge kit is needed, the rotary valve’s supplier can recommend the best venting device for an application or a specific valve.

What’s in a Rotary Valve Seal Purge Kit?

Because of their capabilities, pneumatic conveying systems often incorporate airlocks with a labyrinth-style shaft seal. Purge kits work well with these types of non-contact seals, as they help support the valve’s normal operation. The labyrinth seal is mounted on the outside of the valve and fitted around the shaft. Like a standard purge seal, they are used with compressed air to maintain a seal around the shaft that prevents the product from within the valve from leaking out..

Rotary valve seals, purge kits for labyrinth seals, normally consist of:

  •  Solenoid that uses an electrical signal to turn the air on and off.
  • Filter or regulator that helps regulate pressure and keep air clean.
  • Gauges or flow meters that assist with the delivery of compressed gas.
  • Various fitments like tubing, couplings, clips, and brackets.

Benefits of Purge Kits for New Rotary Valves

There are two basic types of air purging kits for rotary valves that help lengthen the life of a rotary valve. Seal purge uses compressed air distributed around the shaft using a lantern ring. The air is "pushed" through the valve's cover plate to prevent contamination of the seal. When it comes to a new rotary valve, seal purge kits are often used in industries that process abrasive or extremely fine materials, with the pressurized air preventing premature wear around the bearings and shaft seal. Though not used for drier product passing through a rotary valve, seal purge kits can also be used for a wide array of other applications. For example, they work well for facilities where dust is a problem. The purge kit would reduce the risk of hazardous powders escaping the valve into the general plant area, causing an exposure risk to plant personnel and costing more money to maintain cleanliness.

The pocket air purge kit clears the rotor area using compressed air while preventing material buildup within these pockets. Rotor pocket purge kits work best when handling sticky materials. You want to avoid using them on abrasive materials, it will contribute to wear. Avoid flaky materials, it can cause attrition or breakdown of the flake. Air purging extends the operating life of rotary valves, minimizes waste, and offers a means to predict when maintenance is needed. 

Considerations When Choosing a Rotary Valve Seal Purge Kit

A rotary valve maintains a pressure differential between two points within a material handling system, sealing airflow between the inlet and outlet to keep material flowing efficiently through a processing system while also keeping a facility safe from conflagrations or explosions due to dust. In addition to this task, rotary valves are the most common means for feeding pneumatic conveying systems.

Most commonly, a valve will be equipped with either a shaft seal purge kit on its own or with both this and a rotor pocket purge kit. Very occasionally, rotor pocket purge kits are used on their own. These rotary valve seal purge kits are considered essential accessories within a pneumatic conveying system, particularly for applications that involve the processing of finer bulk materials.

Seal purge kits are designed to protect the shaft for a rotary valve. For some applications, these shaft seal purge kits may suffice, while in other cases, it may be desirable to equip a rotary valve with both types of purge kits. In rarer cases, a rotor pocket purge kit may be used independently. For handling bulk powders, a rotary valve purge kit provides the system with a durable, dust-tight seal on a rotating shaft, even for applications that don’t require a pressure differential. As mentioned earlier, continuous or intermittent air pulses from these kits can also be used to purge product from the rotor pockets at the valve’s outlet.

Saving Money When Purchasing a Purge Kit

For a rotary valve, seal purge kits ensure material keeps running through the system smoothly, so it’s important to keep them well-maintained. With the close tolerances involved in a high-quality rotary valve, seal purge kits increase efficiency throughout the whole conveying system.

However, once clearances increase to a certain point between the rotor and the housing through wear, it’s usually time to change the rotor. Many rotary valves used as feeders already come equipped with purge kits, so purchasing a valve that already includes one will normally offer some cost savings. For more specific, in-depth information about how to save both time and money with a specific purge kit for a rotary valve, it’s a good idea to contact the manufacturer directly.

Safety Protocols for New Rotary Valves & Purge Kits

Like any moving piece of equipment, a new rotary valve should be handled according to the manufacturer’s guidelines to prevent accidents that can lead to equipment damage or injury. A good place to start is by reading the equipment manuals containing the manufacturer's instructions on installing the rotary valve and seal purge kit and how it should normally operate. These instructions should be followed carefully and in order, with any unclear instructions followed up by contacting the valve’s manufacturer.

Below are some basic safety protocols for installing and operating a new rotary valve and purge kit:

  • Training: Operators, maintenance staff, and others who may have to work with the new rotary valve should receive sufficient training so that they’re familiar with the equipment and protocols necessary for its safe operation, with training updated and repeated regularly. 
  • Start-up: Once installed, the manufacturer’s instructions should be followed for starting operation, while monitoring should be done to note any possible anomalies.
  • Protective gear: Personal protective equipment (PPE) like earplugs, gloves, and safety goggles should be worn as required during installation and operation.
  • Monitoring: For equipment like a rotary valve and seal purge kits, it’s important to track equipment pressure and temperature; should the machine behave erratically, operators should also be trained to shut it down safely.
  • Maintenance: It’s important for maintenance staff and operators to know the appropriate lockout/tagout procedures, as the manufacturer advises preventing the rotary valve from starting up accidentally while it is being maintained.
  • Inspections: Before installation, both the rotary valve and seal purge kit should be inspected to ensure they’re neither damaged nor their parts defective; should there be an issue, the manufacturer should be contacted immediately. Inspections should also follow regularly to recognize and resolve any issues, with some rotary valve manufacturers even offering preventive maintenance servicing.
  • Emergency procedures: Should the rotary valve malfunction, it’s important that operators know how to shut the machine down safely in an emergency, which includes following appropriate lockout and tagout procedures to ensure all energy sources are isolated and no power is present in the system during maintenance or repair.
  •  Electricity: The rotary valve should be disconnected from its power source during installation and maintenance.
  • Documentation: Detailed records should be kept that include when the rotary valve was installed, along with any inspection dates; the inspection log should include any remedial actions taken like maintenance, modifications or repairs to the system. 

While safety protocols will differ depending on the equipment manufacturer, it’s important to follow these exactly so as not to void any warranties. Additionally, any local, state, or federal regulations regarding industrial equipment should be followed as well. Above all, it’s important always to follow the manufacturer’s guidelines when installing and operating a new rotary valve and seal purge kit.

For more information on the best purge kit to use for your rotary valve or to learn more about our products and services, contact the rotary valve experts at Prater Industries.