This document discusses ergonomic considerations for reducing physical demands when operating valves. It evaluates valve torque requirements, tools that can reduce required force, human force capabilities, and optimal valve positioning and design. The goals are to prevent overexertion and repetitive motion injuries by controlling risks and ensuring valve operation stays below human strength limits. Tools like pneumatic actuators, extended handles, and wrenches can help reduce required forces and improve body mechanics. Proper valve placement and orientation also influences exertion levels.

1. Ergonomics –
Valve Human Factors
Engineering
Managing the Physical Force
Operators are Required to
Apply
Dale Rhodes, MSPH, CIH

2. Goals
Reduce/ eliminate worker overexertion
injuries
Reduce/ eliminate worker repetitive motion
injuries
Reduce predictable and controllable risks
preventing reaching 0 recordable injuries.

3. Knowledge Required
1. What valve turning forces are required?
2. What is the safe strength capacity of the
lowest 95th percentile of the work force?
3. What variables can be controlled to
reduce force requirements to meet #2?
4. What tools and design features need to
be used to control the variables?

4. Valve Actuators
Automatic actuators:
– used to operate valves automatically and/or remotely.
– Automatic actuators typically use pneumatic, electric
or hydraulic power to actuate a valve shaft.
Manual actuators:
– levers or wheels used to transfer physical force from
the human operator to valve shaft directly or through
mechanical gearing or hydraulics.

5. Torque and Force

6. Valve Stem Torque Requirements
Actuator force output requirements
– must be sufficient to overcome valve static friction and dynamic
torque.
Static friction:
– developed in the metal-to-metal surfaces, seats, and seals.
Dynamic torque:
– unbalanced force of the process acting on the plug, disc, or ball.
Valve torque requirements:
– supplied by the manufacturer and based on pressure drop
across the valve. A minimum of 10-20% safety factor should be
applied to the maximum predicted force requirement to insure
reliable operation.

7. Manufacturer Standards
Manufactures Standardization Society of the
Valve and Fittings Industry, Inc. – “Guidelines for
the Operation of Valves SP-91”
– Typical Operator defined as capable of applying
150# of force based on a 12 inch lever.
– Valve designs standards allow for up to 240# of
required force (18” hand wheel) depending on
wheel size
– Do suppliers even belong to or subscribe to this
minimal protective standard?

8. Real World – Required Valve Force
Few field studies of required valve turning
forces exist
1992 study; 217 random chemical plant
valves – 93% could be cracked open with
a 3 ft long wrench using 100# or less
force. 7% could not!

9. Real World - People
1995 study 250 male & female college students, data for
optimal valve orientation, 16” wheel
– Males could apply 123 – 127.5# peak force by hand
– Females could apply 73 – 100# peak force by hand
1997 study
– males could only apply 45 – 55# of sustained force by hand
when turning a valve through 60 deg/sec.
Typical real world required manual valve actuation force
is a miss-match with human capabilities.
= Injuries which = not meeting safety metrics goals

10. Human Operator Force Capability
Variables Affecting Force an Operator can Apply:
whether a wheel, lever or T-lever hand control is used
the shape of that control and effective lever length or
wheel diameter.
the horizontal and vertical position of the valve with
respect to the operator
the distance from the operators vertical line of balance.
the angle of the valve control with respect to the horizon
Adjustments need to be made in maximum acceptable
valve actuation force for each of these factors.

11. Grip Strength Factors
Grip strength magnitude affects the torque that can be
transferred to the hand control and valve stem.
For small single hand operated valves, triangular rather
than traditional round handle shapes reduce gripping
force required by a factor of three for a given amount of
applied torque. Square, star, oval and other non-round
shapes are also advantageous to application of force.
Max. grip strength for small single hand operated valves
with round handles is achieved when the diameter in
kept near average palm grip size of 8 to 9 cm (3 to 3.25”)
with gloved hand.
For larger rim grip valve wheels, the maximum grip
strength is achieved when the rim profile diameter is
about 32 mm (1.25”) for gloved hands.
Gripping aids like wide bumps and spokes improve
applied wheel force by reducing grip effort.

12. Work Practices Risk Factors
Reduce force required. Use protocols that decrease
physical risk and use body mechanics to greatest
advantage. (Safety in Motion).
Always ramp up applied hand/arm force slowly to a valve
handle rather than instantly. Force increase = 26%.
Common practice of sudden high force sudden injury
Use “grippy” gloves that increase grip allowing more
efficient force transfer (up to 15% increase)
Use wrenches! This decreases force required (torque vs.
force formula)

13. Human Force Capabilities as
Function of Large Valve Location
5th Percentile force in Lbs for 57
random male subjects
Presented as a function of valve
wheel height and angle.
Hand to valve wheel turning
Other data indicates female
strength at 45% of male values.

14. Valve Location Factor
Valve angle and layout can contribute
greatly to ease or difficulty in turning the
valve
Leave adequate room for valve wrench
use for both large wheel valves and small
“hand” valves!!
Small hand valves have different
orientation considerations than large
valves

15. “Hand” Valve Positioning
Common hand valve
placement or mode of use
doesn’t match the hand/
wrist safe working range
Operation with
wrist at ≥30o
vertical bend
contributes to
carpal tunnel
and other
hand/arm injury

16. “Hand” Valve Positioning
“Hand” valves which can only be accessed in
front of the operator must be placed or angled to
allow wrists to have less than a 30o bend.

17. “Hand” Valve Positioning
If at all possible a small handled “hand” valve
should be oriented so the stem forms a near 90o
angle with the extended arm.
The ideal small handle can be grasped like a
comfortable hand shake.

18. “Hand” Valve Positioning
Turning a small handled valve
without use of assist tools
always presents some repetitive
motion or strain injury risks.
– Wrist bending during turning motion
– Excessive turning force
Provide valve wrenches
Provide room around valves to
use wrenches
Avoid creating other body
positioning issues
Train operators to reduce risks

19. Help for Small Hand Valves
• Frequently used, difficult to reach valves increase injury risks
• Move them if possible
• Use extension devices/ tools if they can’t be moved
• Bring the point of actuation out to a safe operator position

20. Help for Valves
Similar vertical valves
with and without shop-built
extended “T” handles

21. Help for Valves
Force reducing
portable actuators
– Pneumatic
– Hydraulic
Karmsund Maritime Service
Lakehead
Easi-Drive
E.H. Wachs Co.

22. Help for Existing Valves
Force reducing
portable actuators
– Mechanical Advantage
Lakehead manual ratchet drives

23. Help for Existing Valves
Force reducing, simple
leverage
Valve wheel wrenches
Lever handled valves
Assure good footing, non-slip
platforms
Use where space permits
(potential knuckle busters)