Inst. Calibration Questions

In a reverse acting actuator, everything is the same except…

The diaphragm and actuator stem

What is flashing?

When fluid vaporizes and remains a vapor

What is cavitation?

When fluid vaporizes and returns to a fluid

What happens when liquid passes through an open valve?

pressure decreases and velocity increases

What model number are reverse acting valves?

667

What model number are direct acting valves?

657

What is the direction of a valve determined by?

the direction of the actuator

What is benchset?

the pressure range of air applied to an actuator to make it go full travel with no valve forces present

When is an actuator fully retracted?

at its upper travel stop

What psi value is used to fully retract a reverse actuator

the upper range value; often 15 or 27 psi

What psi value is used to fully retract a direct acting actuator?

the lower-range value; often 3 psi

Damage from cavitation is:

rough

damage from flashing is:

smooth

greater drops in pressure may lead to:

greater cavitation

study value and actuator direction map

What does GPM stand for

gallons per minute

What variable can affect flow rate?

temperature, density, pressure drops, valve size, etc.

What is Cv?( liquid specific)

the number of U.S. gallons water @ 1psi @ 60 degrees for 1 minute

What is the formula for Cv? (draw it out)

In the Cv formula, what does Cv stand for?

flow coefficient

What does QL stand for?

flow rate of liquid (GPM)

What does SL stand for?

specific gravity of liquid

what does ^P stand for

differential pressure (Inlet pressure-outlet pressure)

What is a diaphragm?

a flexible, pressure responsive element that pneumatic control signal is applied to

What is a diaphragm plate?

a rigid plate that the diaphragm pushes against as pressure is increased

What is an actuator stem?

a stem that is connected directly to the diaphragm plate

What is a coupling block?

a block used to join the actuator and valve stem

What does a spring in a valve do?

provides an opposing force to actuator stem as well as an inherent fail mode

what does “valve opening” refer to

relative position of the valve plug to its closed position against the valve seat

What does “Valve throat” refer to?

the actual orifice pass area

What is special about the relationship between orifice pass area and flow rate?

it is a directly proportional relationship

Study handout

Fill in blanks on phone pic of valve

What is valve trim?

the physical shape of the plug and seat arrangement

What is Cv? (general)

flow capability of a valve at full open position

How do you change how far the valve strokes?

change the spring or adjust the spring adjustor

What is HART an acronym for?

Hiway Addressable Remote Transducer

What HART do we use?

475

What is minimum resistance for HART ?

250 ohms

What is the formula for max resistance of HART?

43.5(power supply voltage - 10.5)