Hydraulics/Pneumatics

What is a directional control valve?

A valve with a moveable spool that connects various passages to control the direction of flow

What are the two characteristics a directional control valve is named for?

The number of ports (ways) and the number of positions

What type of DCV only has two positions and wat are they?

A two way valve, blocked and open

What are two way DCVs used for?

Safety interlocks, to isolate or to connect components

What are the ports on a three way DcV?

The tank, pressure and outlet port

What are four way DCVs used for?

Used with actuators (one end connects to pressure while the other vents)

What are manual ways for a spool to be actuated?

Lever, button, foot pedal

What are mechanical ways for a spool to be actuated?

Lever or cam

How does solenoid actuation work for a DCV?

A magnetic field generated by a coil moves a plunger that moves the spool

What are the two types of solenoid acutation?

Air gap or wet armature

What is an air gap solenoid?

The plunger is sealed from the working fluid and air is the cooling medium

What is a wet armatuure solenoid?

The whole plunger is in the fluid and the coil is external, working fluid is the cooling medium

What are common solenoid failures?

Improper seating (excess current = components to melt/coils burn out)

Extreme ambient temp (block heat dissipation and cause burn out)

Dual solenoids with both energized (won’t seat properly)

What are the limitations of solenoids?

They cannot be used in expolsive/wet environments

Coils have a finite life meaning short service life

Only small forces available

How does a pilot operated valve work?

The pilot pressure (hydraulic or pneumatic) provides high force to actuate the spool

What are the benefits of pilot operated DCVs?

No electrical components (can work in explosive/wet/dirty environments)

Reliable operation since it has no coils to burn out

What is a solenoid controlled pilot operated DCV?

A DCV that is actuated by a pilot, and the pilot fluid is controlled by a solenoid valve

What is a spring overset DCV?

A valve that has a spring to push it back to a certain position when not being actuated

What are the different center conditions for a DCV?

Open, Closed, Tandem, and Float

What is an open center?

All the ports are connected to each other

What is a closed center?

All the ports are blocked and ther is no flow

What is a tandem center?

The pressure port goes directly back to the tank

What is a float center?

The pressure port is blocked and all other ports go to tank

What are proportional and servo valves used for?

They are used to meter the output flow proportional to a signal

What is the difference between a servo and proportional valve?

Proportional valves are less expensive and more tolerant of dirt but slower to respond

How is a proportional valve operated?

Electrionic feeback control adjusts the spool position to match the input

How are servo valves operated?

Spool is moved by a torque motor and is given feedback via a spring

What is the value of atmospheric pressure?

101.325 kPa or 14.7 psi

What are the arangment patterns for …?

Diamond, Flock of geese, Parallelogram

What is free air?

Air that is at the inlet condition of compressor

What types of prime movers are used for compressors?

Commonly used either electric or gas

What are the types of air dryers?

Absorption (drying agent (chalk, magnesium perchlorate, lithium/calcium chloride) combines with water and settles)

Desiccant (water vapour is trapped in pores (can be regenerated by heating))

Refrigerated (lowers air temp to below dew point, condensate is drain (can’t be lower than 0.6 degrees))

What are the classifications of contaminants?

Hard, Soft, Fluid