United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-02: Limitorque HOBC, H1BC, H2BC, and H3BC Gearheads

                                                            SSINS No.: 6835 
                                                            IN 83-02       

                                UNITED STATES
                           WASHINGTON, D.C. 20555
                              January 28, 1983

Information Notice No. 83-02:   LIMITORQUE HOBC, H1BC, H2BC, AND H3BC 


All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 


This information notice is provided as a notification of a potentially 
significant maintenance problem pertaining to Limitorque HOBC, H1BC, H2BC, 
and H3BC gearheads. No specific action is required in response to this 
information notice, but it is expected that recipients will review the 
information for applicability to their facilities. 

Description of Circumstances: 

In its letter of January 10, 1983, Limitorque advised the NRC of a recent 
experience with a type H3BC gearhead on a butterfly valve at a municipal 
water treatment plant. Although it involved a maintenance problem, rather 
than a design deficiency, Limitorque still considered it to fall within the 
10 CFR Part 21 criteria because similar gearheads are used in the nuclear 

The H3BC gearhead was being adjusted to set the mechanical stops in the open
position. The H3BC gearhead is equipped with a worm gear segment so as to 
accommodate the 90 degree travel of a butterfly valve, and contains 
mechanical stops driven by the worm gear. In the process of setting the 
mechanical stops, the maintenance contractor's personnel at the plant did 
not orient the worm gear segment precisely with the valve travel, as called 
for in Limitorque's maintenance bulletin instructions. (This is a unique 
circumstance because the actuator was field installed on the butterfly valve
so that the valve manufacturer did not have the opportunity to properly 
reset the mechanical stops.) The result was that the worm gear segment was 
rotated beyond its engagement with the worm shaft. The butterfly valve disc 
was then free to react to hydrostatic forces that caused it to move suddenly 
to the closed position as full flow existed in the pipeline at the time. 

Limitorque has suggested that all plant maintenance personnel be alerted to 
this possibility. Each of the standard size HOBC, H1BC, H2BC, and H3BC 
gearheads are similarly equipped with a worm gear segment and worm shaft 
actuated mechanical stops. These gearheads may be used on manually operated 
valves or coupled with various sized limitorque SMB type actuators for power
operation. Should field maintenance be performed on any of these size 
gearheads, the maintenance personnel involved should be cautioned to orient 
the worm gear segment with the butterfly valve travel as called for in 
Limitorque's maintenance instructions. These instructions describe the 
procedure for orienting 


                                                          IN 83-02        
                                                          January 28, 1983 
                                                          Page 2 of 2     

the index mark on the drive sleeve (gear segment centerline) with the 
midpoint of valve travel. Limitorque is in the process of" adding a more 
specific caution note to its maintenance instruction manual (HBCI-81) for 
this type of actuator. A sample of this revision is enclosed as Attachment 

It should be noted that the larger sizes of gearheads (H4BC through H10BC) 
do not have this potential problem as the drive sleeve mechanical stop 
adjustment range will not allow the worm gear segment to rotate free of the 
worm shaft. 

No written response to this notice is required. If you have any questions 
regarding this matter, please contact, the Regional Administrator of the 
appropriate NRC Regional Office, or this office. 

                                   Edward L. Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Richard J. Kiessel

1.   Revised page 4 of Limitorque's Maintenance Instruction
     Manual HBCI-81
2.   List of Recently Issued IE Information Notices

Page Last Reviewed/Updated Friday, May 22, 2015