Information Notice No. 82-56: Robertshaw Thermostatic Flow Control Valves

                                                            SINNS No.: 6835 
                                                            IN 82-56 

                               UNITED STATES 
                           WASHINGTON, D.C. 20555 

                             December 30, 1982 



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 problem pertaining to Robertshaw Thermostatic Flow Control 
Valves. No specific action is required in response to this information 
notice, but the manufacturer in 10 CFR Part 21 correspondence with the NRC 
has requested that the NRC advise the nuclear industry of a potential 
problem with application of three versions of flow adjustment subassemblies, 
since substantially identical units are sold commercially and may have been 
purchased through distributors without identification that the end use is in
a nuclear power plant. 

Description of Circumstances: 

Robertshaw Thermostatic Flow Control Valves are widely used for temperature 
control in fluid systems. Among other uses, Robertshaw has supplied Model 
1284 and Model 1285 valves to manufacturers of diesel engines which power 
emergency generators for nuclear power plants. Details of the systems may 
vary, but in general, the engine cooling fluid flow path is either directed 
through a cooler or diverted around it by modulating action of the valve in 
response to coolant temperature sensed at the valve inlet. The valve stroke 
is set by a nut on a threaded stem. If that nut backs off, the temperature 
setpoint is significantly lowered. Running a diesel engine with excessively 
low coolant temperature may lead to engine damage. 

The valve stem nut in the original design was staked in place at the factory
on assembly. In 1977 a customer reported that the nut on one assembly had 
completely disengaged; subsequently, the same customer reported a similar 
occurrence on another assembly. Manufacturing records showed that both 
assemblies had been made on the same day by a single mechanic. To provide 
better assurance that the nut would stay in place, the manufacturer changed 
the assembly procedure to lock the nut by soldering with lead-tin solder. 
Recently, the manufacturer became aware that some "corrosion inhibitors" 
used in closed cooling, water systems aggressively attack lead-tin solders 
(IE Circular 80-11). Based on this information, the manufacturer further 
revised assembly procedures to use of a castellated nut and cotter pin, 
eliminating use of lead-tin solder. 


                                                           IN 82-56  
                                                           December 30, 1982 
                                                           Page 2 of 3 

Since there has been only the one reported failure, none of the above 
described assembly modifications were considered by the manufacturer to be 
of sufficient significance to warrant production retrofit, except for valves
specifically identified as destined for use on emergency diesel generators 
for nuclear power plants. The manufacturer believes that many valves in 
service have been assembled by one of the now-obsolete techniques. Because 
of the wide distribution and use of these valves, some may be in use in 
safety-significant applications. This in itself may not be a problem since, 
depending on use, the postulated failure mode may be acceptably "fail safe."

Another design feature of the subject valves is the use of a modified "O" 
ring to control bypass leakage within the valve when the valve is positioned
to divert flow from the cooler. A cylindrical valve plug controls the fluid 
flow out of one or both of the discharge ports by moving axially. The "O" 
ring floats in a groove in the valve body web and is around the valve plug. 
It limits bypass leakage to about 1 percent of full flow. 

Thermal element (valve actuator) power available to position the valve plug 
is small, and the dimensions of the "O" ring and the groove are such that 
there is no preload on the "O" ring. Instead, the "O" ring has been cut and 
a small section of the ring has been removed to assure that the ends do not 
make contact. In one instance, contamination of the coolant by diesel fuel, 
caused by a faulty fuel injector, resulted in swelling of the "O" ring, 
which prevented normal movement of the valve plug. Evaluation of this event 
resulted in the manufacturer recommending elimination of the "O" ring for 
emergency diesels in nuclear power. The basis for this recommendation is the
stated practice of maintaining the engine at an elevated temperature at all 
times that it is in a standby condition. Therefore, the slightly increased 
bypass flow through the cooler is considered to be acceptable during the 
startup transient. As soon as the engine picks up load and begins to reject 
heat, the valve opens to allow partial flow through the cooler, and the 
"bypass" flow becomes unimportant. The validity of this analysis has been 
confirmed by the engine manufacturer. 

A similar situation exists with other applications of the subject valve. 
Depending on circumstances a licensee may or may not decide that prudence 
dictates replacement of the stroke adjustment assembly and/or removal of the
split "O" ring. 

                                                           IN 82-56 
                                                           December 30, 1982 
                                                           Page 3 of 3 

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 Engineering and  
                                Quality Assurance  
                              Office of Inspection and Enforcement 

Technical Contact:  J. B. Henderson 

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