Checking Clearances

Checking Rotary Valve Clearances

Rotary valves are precisely machined to accommodate very tight internal clearances. In a smaller standard valve there should be a .003” – .005” gap between the tips and ends of the rotor and the housing / headplate. However, the clearances on many valves are customized to meet the needs of a specific application. For example, in applications with temperature greater than 70°F, the clearances may need to be larger to allow for thermal expansion. Before examining the valve, contact Wm. W. Meyer & Sons to find out what internal clearances your valve was configured with.

It is important to maintain tight clearances; this allows the airlock valve to effectively create a seal, while maintaining a flow of material between components with different pressure. However, just like anything else, rotary valves wear out too. The lifespan of a rotary valve typically depends on the characteristics of the material going through it, the features it was constructed with, the application it is used in, and the amount of preventative maintenance performed. Some valves remain in service for 30+ years without wearing out. Others need to be replaced or rebuilt several times a year. Typically valves operating in abrasive environments have shorter life spans.

There are two main reasons one would need to check the clearances on a rotary valve. Either the valve is making a sound indicative of the rotor coming into contact with the housing, or symptoms of air leaking through the valve are present. However, if a new valve is making a high pitched noise, several things should be done before checking the clearances.

  • First, check with the supplier of your valve to find out what temperature your equipment was manufactured to accept. If the material going through the airlock is at a higher temperature than the valve was built to handle; checking the clearances will not solve the problem.
  • Next, make sure the rotary valve is level. The airlock should be bolted to a perfectly flat surface on top and bottom. The slightest amount of torsion could deplete the extremely small internal clearances, causing the rotor to come into contact with the housing or headplate.

Regardless of the reason why the clearances need to be checked, the same procedure should be used. Listed below are step by step instructions, but before getting started, make sure to gather the tools necessary to complete the task.


  • Lockout-Tag out Padlock
  • Pair of Needle Nose Pliers (or tool for removing chain links)
  • Phillips Head Screw Driver
  • Set of Feeler Gauges .001 – .015

CAUTION: Rotary valve maintenance should only be performed by authorized personnel.

DANGER: Before beginning any work on the rotary valve, make sure that the circuit breaker that controls incoming power to the gearhead motor are LOCKED OFF.

1. Remove the feeder from the installation to gain access to the top and bottom of the feeder.
2. Remove the chain guard.
3. Remove the chain from the feeder sprockets.
4. Clean out any material from the inside of the valve.
5. Get out the size feeler gauge that matches what the minimal clearance should be. For example, if your valve should have clearances from .007” – .009” get out the .007” feeler gauge.
6. Insert the gauge between the end of the rotor vane and head plate on the drive end of the valve. Then slide it down to the shaft of the rotor and back up to the tip of the rotor. As long as the gauge slides freely, remove the feeler gauge, and repeat the process on the blind end of the valve.
7. Rotate the rotor in the direction that it normally turns so that the next vane is accessible through the inlet. Repeat step 6 until all of the ends of the vanes have been checked.
8. Now check the tips of the rotor. To do this, slide the feeler gauge between the tip of the rotor and the housing. Slide the feeler gauge from one headplate all the way over to the other.
9. Rotate the rotor in the direction that it normally turns and check the clearances on the tips of all the rotor vanes.
10. Get out the feeler gauge that is .001” greater than what the high end of the clearance should be. So if the valves clearances should be .007”- .009”, you will want to pull out the .010” feeler gauge.
11. Attempt to insert the .010” feeler gauge between the ends of the rotor and the headplate, and try to insert it between the tips of the rotor and the housing. The feeler gauge should not fit, and if it does, either the housing and headplate or rotor has begun wearing out.
12. Now check the clearances through the outlet.
13. Insert lifting lugs into the bolt holes on the inlet flange. Put a strap through the lugs and use a hoist to carefully lift the valve.
14. Going through the discharge flange repeat steps 5-11


If the clearances on the valve are within specification, it is time to return your valve to service. If the clearances are too big or small, Contact Us to get a solution.