SACA Pneumatic and Hydraulic Systems 2

Question 1

What is the function of an 'FRL' (Filter-Regulator-Lubricator) unit in a pneumatic system?

Accepted Answer

It conditions compressed air by removing contaminants (filter), setting working pressure (regulator), and adding oil mist for cylinder/valve lubrication (lubricator)

Answer

It converts high-pressure air to electricity for pneumatic control systems

Answer

It measures and records air consumption for energy management purposes

Answer

It converts compressed air pressure to an analog 4-20mA signal for PLC input

Question 2

In a hydraulic system, what is the purpose of a 'relief valve' and where is it typically installed?

Accepted Answer

To limit maximum system pressure by venting excess flow back to tank when pressure exceeds the set value, preventing component damage and burst lines

Answer

To relieve the operator from manually opening and closing the main pump bypass valve during startup

Answer

To control the speed of a hydraulic cylinder by throttling flow on the return line

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To provide a pressure signal to the PLC when a cylinder reaches end of stroke

Question 3

What is 'hydraulic lock' in a cylinder circuit and how does a 'pilot-operated check valve' prevent unwanted cylinder drift?

Accepted Answer

Hydraulic lock is the condition of trapping oil in both cylinder ports to prevent drift; a pilot-operated check valve allows flow in one direction freely, and in the reverse direction only when a pilot signal opens it

Answer

Hydraulic lock is when oil freezes in cold conditions; pilot-operated check valves add heaters to maintain oil temperature

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Hydraulic lock describes pump seizure from contaminated oil; pilot-operated check valves filter oil at the pump inlet

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Hydraulic lock is control valve overlap condition; pilot-operated check valves compensate with adjustable overlap settings

Question 4

In pneumatic systems, what does 'flow control valve' accomplish, and what is the difference between meter-in and meter-out circuits?

Accepted Answer

Flow control valves throttle air flow to control cylinder speed; meter-in restricts flow entering the cylinder (inlet control); meter-out restricts flow leaving the cylinder (exhaust control)

Answer

Flow control valves adjust the air pressure supplied to cylinders; meter-in increases pressure at the cap end; meter-out decreases pressure at the rod end

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Flow control valves filter contaminants from compressed air; meter-in uses fine filters; meter-out uses coarse filters

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Flow control valves switch between single-acting and double-acting cylinder modes based on pressure

Question 5

What is a 'proportional directional control valve' (PDCV) and how does it differ from a standard solenoid directional valve?

Accepted Answer

A PDCV uses an analog command signal (0-10V or 4-20mA) to continuously vary the valve spool position and thus flow rate — standard solenoid valves switch only between two discrete positions (fully open/fully closed)

Answer

A PDCV has three or more solenoids for additional port positions; standard valves have only two positions

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A PDCV includes an integrated pressure relief valve; standard valves require external relief protection

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A PDCV can be operated manually; standard valves are solenoid-only with no manual override

Question 6

What is 'cavitation' in a hydraulic pump and what conditions cause it?

Accepted Answer

Formation of vapor bubbles in the hydraulic oil due to low inlet pressure (below oil vapor pressure), followed by violent implosion causing erosion and noise when bubbles enter higher-pressure regions

Answer

Metal particles eroding pump vanes caused by inadequate lubrication at startup

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Air entrainment from a loose intake hose fitting causing foamy oil and reduced pump efficiency

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Thermal expansion of oil at high temperature causing pump housing distortion and internal leakage