Hydraulics, Pneumatics, and Industrial Maintenance Flashcards

Fundamental Principles and Rules of Hydraulics

• Typical Maximum Hydraulic Pressure: Industrial hydraulic systems typically operate at a maximum pressure of approximately $3000\,psi$.

• Leak Detection Methodology: The safest and most effective way to check for leaks in a hydraulic line is to use a piece of paper, never hands, to avoid high-pressure injection injuries.

• Bottle Jack Operation and Stroke Limits: If a bottle jack is stroked out to its maximum extension, it is still possible to pump it. This is because bypass vanes located in the threads allow the fluid to bypass back into the reservoir rather than causing mechanical failure.

• Liquid Compressibility: Liquids are considered incompressible for most practical purposes. However, they technically compress by a negligible amount of approximately $0.5\%$ for every $1000\,psi$ of applied pressure.

• Gas Compression and Heat: Unlike liquids, gases are highly compressible. When gases are compressed, the kinetic energy results in the creation of heat.

• Atmospheric Pressure: The standard atmospheric pressure of air at sea level is precisely $14.7\,psi$.

• Flow Definition and Measurement: Flow refers to the volume of fluid being pumped over a specific duration. It is typically measured in Gallons Per Minute (GPM) or Liters Per Minute (LPM).

• Velocity Definition and Measurement: Velocity is the distance traveled by a fluid over a given time interval, measured in units such as inches per second or inches per minute.

• Turbulent Flow and Pressure Drop: Friction within hydraulic lines creates turbulent flow, which generates heat and leads to a subsequent drop in system pressure. Laminar (smooth) flow is the desired state.

• The Seven Rules of Hydraulics:   - Oil will flow in any direction and through passages of an infinitely small size.   - Cleanliness is of paramount importance because small passages can be easily blocked by contaminants.   - Pumps create flow, not pressure. Pressure is created only by restrictions to that flow.   - For flow to occur, there must be a difference in pressure, known as a pressure differential ($P/D$).   - The three primary controllable factors in a hydraulic system are flow, pressure, and direction.   - Flow determines the speed of an actuator. An ideal flow velocity for hydraulic lines is $15-20\,ft/sec$.   - Relationship of Force, Pressure, and Area ($Flying over PA$):     - Force (F) equals Pressure (P) multiplied by Area (A): $F = P \times A$.     - Pressure (P) equals Force (F) divided by Area (A): $P = \frac{F}{A}$.     - Area (A) equals Force (F) divided by Pressure (P): $A = \frac{F}{P}$.

• Cylinder Surface Area Calculation: The surface area of a cylinder is calculated using the formula: $\pi \times r^2$.   - Example: For a $2.5\,\text{inch}$ shaft, the area is approximately $4.9\,in^2$. If there is $10\,lbs$ of pressure, the resulting psi is $\frac{10}{4.9} = 2.04\,psi$.

• Leverage and Ratios: If a $10\,\text{inch}$ shaft is driven by a $1\,\text{inch}$ shaft, the ratio is $10:1$. Applying a $100\,lb$ force on the small piston results in $100 \times 10 = 1000\,psi$.

Mechanical Advantage and Levers

• Classes of Levers:   - First Class: The fulcrum is located between the effort and the load ($Effort - Fulcrum - Load$).   - Second Class: The load is located between the effort and the fulcrum ($Effort - Load - Fulcrum$).   - Third Class: The effort is located between the load and the fulcrum ($Load - Effort - Fulcrum$).

• Effort Calculation: The Effort (E) multiplied by the Effort Arm (EA) equals the Load (L) multiplied by the Load Arm (LA). Formula: $E \times EA = L \times LA$.   - Example: Given a $12\,\text{inch}$ EA, a $6\,\text{inch}$ LA, and a load of $100\,lbs$. $E \times 12 = 100 \times 6$. Solving for E: $E = \frac{100 \times 6}{12} = 50\,lbs$ of effort.

• Mechanical Advantage (MA): MA is calculated as the ratio of the effort arm to the load arm ($\frac{EA}{LA}$). In the example above ($\frac{12}{6}$), the MA is $2:1$.

Fluid System Design and Control Circuits

• Positive Displacement Protection: All systems utilizing a positive displacement pump must incorporate a relief valve to prevent catastrophic pressure buildup.

• Vacuum Definition: A vacuum is defined as any condition where the internal pressure is lower than the local atmospheric pressure.

• Circuit Metering Strategies:   - Metering In: Placing a flow control valve on the inlet to the cylinder to regulate incoming flow. This is primarily used for opposing loads but carries the risk of a runaway load pulling the piston ahead of the oil supply.   - Metering Out: Placing a flow control valve on the outlet of the cylinder. This prevents runaway loads but can cause pressure intensification. For example, $1000\,psi$ entering a cylinder may result in $2000\,psi$ at the rod end on a $2:1$ ratio.   - Bleed Off Circuit: T-ing a flow control valve to the tank on the main line. This controls flow but will not prevent runaway loads.

• Flow Control Valve Types:   - Non-variable Fixed Orifice: An inexpensive orifice plate used similarly to a "farmer fix" to control basic cylinder speed.   - Variable Flow Control - Restrictor: Restricts flow and redirects the excess across the Pressure Relief Valve (PRV). This wastes energy; flow varies significantly with workload changes.   - Pressure Compensated Restrictor: Maintains constant flow regardless of workload changes by automatically compensating for pressure fluctuations. Suitable for meter-in, meter-out, or bleed-off circuits.   - Pressure Compensated Bypass: Similar to the restrictor, but excess flow is redirected to an EX port to the tank rather than the PRV, saving energy and reducing heat. It requires back pressure and should only be used in meter-in circuits between the pump and the Directional Control Valve (DCV).

• Cylinder Vulnerability: The rod seals are universally considered the weakest part of a hydraulic cylinder and are typically the first failure point.

• Pressure Gauges: Gauges are designed to read downstream pressures.

Hydraulic Pump Technology

• Pump Function: A pump's sole purpose is to create flow. Pressure only develops when that flow encounters resistance.

• Unit Comparison: One US Gallon Per Minute (USGPM) is equivalent to $231\,in^3$.

• Power Requirements: Increasing flow requires an increase in horsepower, which typically necessitates a larger electric motor.

• Pump Classifications:   - Fixed Displacement: Moves the exact same volume of fluid with every revolution.   - Variable Displacement: Allows for the adjustment of flow volume without stopping the pump.

• Flow Expression: Pump flow is expressed via displacement (volume per rotation) or GPM.

• Gear Pump Components: Consists of a driven gear (keyed to the shaft) and an idler gear. Gear pumps are unbalanced due to higher pressure on the outlet side, requiring the shaft and bearings to carry significant loads.

• Gear Pump Operation: As teeth separate, they create a vacuum to pull fluid in; as they mesh, they push fluid out. Side plates maintain internal pressure.

• Lubrication: Fluid left between teeth enters decompression notches, channelling it to grooves that lubricate the bearings.

• Internal Gear Pumps:   - Crescent Type: Uses a crescent-shaped seal machined into the body to separate the inlet and outlet ports.   - Gerotar: Features an internal gear with one less tooth than the outer gear, relying on extremely tight tolerances rather than a crescent seal.

• Vane Pumps: Features vanes slotted into a rotor spinning within an eccentric cam ring. Centrifugal force and high-pressure fluid supplied under the vanes keep them extended. Unbalanced vane pumps are offset; balanced vane pumps use an oval cam ring with two intakes and two discharges to neutralize loads, doubling the fluid displacement.

• Pressure-Based Selection:   - Systems up to 3000 psi: Typically use vane and gear pumps.   - Systems above 3000 psi: Exclusively use piston pumps.

• Threads: The most common thread type on pumps is ORB (O-Ring Boss).

• Contamination Resistance: Gear pumps are best suited to handle contaminated fluids.

• Variable Applications: Variable displacement piston pumps are the industry standard for applications requiring adjustable flow.

• Hydrostatic Systems: A closed-loop system offering superior control for starts, stops, and direction. All hydrostatic systems are hydraulic, but not all hydraulic systems are hydrostatic.

• Radial Piston Pumps: Arranged like a helicopter's radial engine. The outer ring is offset to drive pistons. These are excellent for low-speed, high-torque applications.

• Speed vs. Torque in Piston Pumps: Decreasing the speed of a piston pump increases the torque it can deliver; increasing speed decreases torque.

• Piston Pump Types:   - Bent Axis: Pistons are mounted at an angle via ball joints to achieve stroke.   - In-line: Pistons connect via shoes to a swash plate. Changing the angle of the swash plate adjusts the stroke length and displacement.

• Variable Displacement Benefits: Eliminates wasted energy and heat by only pumping what the system requires, rather than dumping excess over a PRV.

• Pressure Compensator: A mechanism that uses high-pressure fluid to actuate a yoke and change the swash plate angle. High pressure brings the angle closer to zero, limiting flow.

System Valves and Directional Controls

• Six Types of Pressure Control Valves:   1. Relief valve   2. Unloading valve   3. Pressure reducing valve   4. Counterbalance valve   5. Sequence valve   6. Brake valve

• Standard adjustment: Most valves use a spring and screw mechanism.

• Valve States:   - Cracking Pressure: Pressure at which the poppet first lifts to divert flow.   - Full Flow Pressure: Pressure when the valve is diverting its maximum flow capacity.   - Pressure Override: The difference between cracking pressure and full flow pressure.

• Pressure Relief Valve (PRV): Limits maximum system pressure. Direct PRVs use large springs and create significant heat. Pilot-actuated PRVs use an orifice and a balanced piston for higher efficiency.

• Unloading Valve: Uses remote pilot pressure to redirect flow to the tank in hi/low applications.

• Pressure Reducing Valve: Normally open; it limits pressure in a specific downstream portion of the system. It features a pilot line leading ahead of the valve and usually includes a case drain.

• Sequence Valve: Directs flow to a secondary actuator only after a set pressure is reached (e.g., clamp then drill setups). It has a case drain to the tank.

• Counterbalance Valve: Counteracts weights or overrunning loads. It limits pressure intensification during metering out and is typically shown with a check valve.

• Bake Valve: Used with hydraulic motors for dynamic braking. It has two pilot lines and an $8:1$ ratio piston to prevent system damage. Includes a check valve.

• Directional Control Valve (DCV) Centers:   - Closed Center: Blocks all ports in neutral; keeps pressure available for other circuit parts.   - Open Center: All ports connect to the tank in neutral; allows motors to wind down.   - Tandem Center: Connects Pump ($P$) to Tank ($T$) while blocking working ports; common in log splitters.   - Float Center: Allows an actuator to move freely (float).   - Regenerative Center: Used for high-speed extension by equalizing area around the rod; results in lower force.   - Transitory DCV: Acts as a 2-position valve that passes through center positions without stopping, preventing sudden shock in high-flow systems.   - Infinite Position Valve: Allows throttling between positions.

• Two-Stage Pilot DCVs: Used for high flow/pressure. Controlled by a pilot solenoid. Troubleshooting involves checking for manual operation, resistance via multimeter (shorts/opens), or continuity to ground.

• Stacked DCVs: Solenoid-operated valves mounted on a manifold with O-rings, reducing the total number of connections.

Conductors, Fittings, and Fluids

• Conductor Sizing:   - Pipe: Sized by nominal Inside Diameter (I.D.) up to $14\,\text{inches}$; over $14\,\text{inches}$, O.D. is used. Use only seamless pipe for hydraulics, primarily for return lines. Must be pickled (cleaned) before use.   - Tubing: Sized by Outside Diameter (O.D.). It is seamless, bendable, and uses flared compression fittings. Do not use thin-walled plumbing tubes.   - Hoses: Sized by Dash Number (#) in increments of $1/16^{\text{th}}$. Example: $-8 = \frac{8}{16} = \frac{1}{2}\,\text{inch I.D.}$. Constructer of oil-resistant neoprene and reinforced with braided wire.

• Hose Installation Pitfalls: Lack of slack, messy routing, kinks, twists, or lack of protection from heat and abrasion.

• Physical Principles:   - Bernoulli’s Principle: Faster moving fluids exert less pressure; slower fluids exert more pressure.   - Pascal’s Law: Pressure applied to a confined fluid is transmitted equally in all directions at right angles to the surface.

• Fluid Velocity and Friction: High velocity causes turbulent flow, leading to friction and heat (pressure drop). Ideal flow in pressurized lines is $15-20\,ft/sec$ at $500-3000\,psi$.

• Fluid Purposes: Lubrication, force transfer, sealing, corrosion prevention, heat dissipation, and contaminant removal.

• Viscosity Index (VI): A measure of how viscosity changes with temperature; a higher VI number indicates less change.

• Types of Fluids:   - Petroleum Oil: Most common, low cost, flammable.   - Fire Resistant: Invert emulsion ($60\%$ oil/$40\%$ water) or glycol-based for extreme cold.   - Bio Oil: Canola/soybean based, expensive, poor temperature performance.   - Synthetic: Expensive, toxic, but offers reduced friction and high-temperature stability.

• Fitting Standards:   - NPT: National Pipe Thread; has a spiral leak path and requires sealant.   - NPTF: National Pipe Thread Fuel; 100% engagement (dry seal). Very common in hydraulics.   - ORB: O-Ring Boss; straight threads for clamping only, seal is provided by O-ring.   - Flared Fittings: SAE ($45^{\circ}$) is for low pressure; JIC ($37^{\circ}$) is the hydraulic standard. They will thread together but WILL NOT hold pressure.

Filtration, Accumulators, and Maintenance

• Hydraulic Failures: $80\%$ are caused by poor fluid condition.

• Filter Locations:   - Strainer: Pre-pump ($100\,\text{mesh}$); requires bypass for cavitation prevention.   - Pressure Line: After pump; must be pressure rated.   - Return Line: Before tank; usually spin-on type.

• Filter Ratings: Nominal (approximate), Absolute (exact spherical diameter), and Beta Ratio (Upstream particles / Downstream particles). A higher Beta number is superior.

• Accumulators: Store pressure and absorb shocks. Loaded by spring, weight, or pressurized Nitrogen (never Oxygen). Pre-charge is usually $50\%$ of max system pressure, set when the system is offline.

• Heat Exchangers: Ideal fluid temperature is $150-180\,^{\circ}F$. Above this, seals degrade and oil oxidizes. Plumb "cool with cool" and "hot with hot" to avoid thermal shock.

• Troubleshooting Sequence: Check fluids and filters first. New pumps must be primed through the case drain.

• Formulas:   - $1\,\text{Hydraulic Horsepower} = 1\,GPM\,\text{@}\,1500\,psi$.   - $\text{Travel Speed} = \frac{\text{Volume}}{\text{Time}}$.   - $\text{Speed (in/min)} = \frac{\text{Flow Rate}}{\text{Area}}$.

Machinery Alignment (Millwright Notes)

• Pre-alignment Checks: Clean base, check runout, ensure MTBS (Machine To Be Shimmed) is lower than fixed unit, check for bolt-bound conditions, shaft endplay, and base cracks.

• Standard Terminology:   - TIR: Total Indicator Reading (half this value for actual calculations).   - Positive Slope: Couplings are further apart at the top.   - Negative Slope: Couplings are further apart at the bottom.

• Methods:   - Rim and Face: Better for large couplings and short distances.   - Cross Dial (Reverse Indicator): Preferred for small couplings, long distances, and electric motors with magnetic centers (rim only, less endplay sensitivity).

• Soft Foot Types:   - Angular: Bad foot; fix with tapered washer/step shim.   - Sprung: Bad baseplate; fix with machining.   - Ordinary: Fix with normal shims.

• Alignment Tolerances: Angular ($0.0005\,in/in$ of diameter), Runout ($0.002\,in$), Soft foot ($0.002\,in$).

• Thermal Expansion: Coefficient of steel is $0.0000063$. Formula: $0.0000063 \times \text{Length (in)} \times \text{Temp Change}$.

• Shim Rules: Use fewest possible, create a "sandwich" (largest on outside), and ensure shims cover the largest foot area.

• Vertical/Horizontal Positioning: Vertical checks at $12$ and $6$ o’clock; Horizontal at $3$ and $9$ o'clock.

• Dial Sag: Add to "A" and subtract from "B" once zeroed.

Pipefitting and Valve Technology

• Steel Pipe Finishes: Black iron (standard), Bare metal (oiled), Galvanized (Zinc coated—toxic to weld, not for hydraulics), Pickled (rust-free for hydraulics), Jacketed (yellow underground gas).

• Threads and Sealants: Use Teflon tape to seal, reduce friction, and prevent galling. White (standard), Pink (thick/large dia), Yellow (gas/Oxygen), Gray (nickel-infused for stainless).

• Joints: Unions should have flow in direction of nut writing. Swage nipples allow reduction without multiple fittings. Swedge nipples eliminate multiple fittings.

• Valve Categories:   - Stop Valves: Globe (throttling, high pressure drop), Gate (isolate only, no throttling), Needle (precise control), Plug/Cock (slurries), Ball (minimal loss), Butterfly (quick isolation/regulation), Diaphragm/Pinch (corrosive/slurry).   - Check Valves: Swing (horizontal), Lift (vertical/piston), Foot (suction line priming).

• Relief vs. Safety Valves: Relief valves are for liquids (normally closed, opens gradually); Safety valves are for gases/steam (normally closed, "pops" fully open).

• Steam Systems: Condensate causes water hammer. Steam traps (Mechanical/Inverted bucket, Thermostatic/Wax canister, Thermodynamic/Disk) separate steam from liquid.

Pneumatics and Air Compression

• Industrial Pressures: Typically $90\,psi$ ($125\,psi$ for shop air).

• Air Composition: $78\%\,N_2, 21\%\,O_2, 0.94\%\,Ar, 0.06\%\,Other$.

• Gas Laws (Use Absolute Values: Rankin $+460$ or Kelvin $+273$):   - Boyle’s Law (Constant Temp): $P_1 \times V_1 = P_2 \times V_2$.   - Charles’ Law (Constant Pressure): $\frac{V_1}{T_1} = \frac{V_2}{T_2}$.   - Lussac’s Law (Constant Volume): $\frac{P_1}{T_1} = \frac{P_2}{T_2}$.   - Ideal Gas Law: $\frac{P_1 \times V_1}{T_1} = \frac{P_2 \times V_2}{T_2}$.

• Compressor Types:   - Dynamic: Axial/Radial flow for high volume, low pressure.   - Positive Displacement: Reciprocating (Piston) or Screw (Wet/Dry).

• Screw Compressor Control (Sullair): VFD (best), Modulation, Load/Unload, Start/Stop.

• Dryers: Absorption (Calcium Chloride, corrosive), Regenerative Desiccant (Silica beads, lowest dewpoint), Refrigeration (Cooling past dewpoint—most common).

• Vacuum: Perfect vacuum pulls $29.92\,inches$ of Mercury ($Hg$).

Industrial Pump Systems and Maintenance

• Classifications:   - Dynamic: Centrifugal (Volute or Diffuser), Axial (propeller), Mixed Flow, Regenerative Turbine (handles $20\%$ vapor).   - Positive Displacement: Rotary (Gear, Vane, Screw, Lobe) and Reciprocating (Plunger, Piston, Diaphragm).

• Pump Height Limits: Theoretical maximum lift is $33.9\,ft$. Practical limits: Centrifugal ($15\,ft$), Positive Displacement ($22\,ft$).

• Head Pressure Definitions:   - Static: Vertical distance of non-moving fluid.   - Dynamic: Static head minus friction losses.   - Total Head: Suction lift plus discharge head.

• Net Positive Suction Head (NPSH): Critical to prevent cavitation (imploding vapor bubbles in the impeller eye).

• Pump Seals: Stuffing boxes (mechanical packing—requires weeping for cooling/lube) or Mechanical Seals (for hazardous/zero leakage).

• Impeller Designs: Open (solids), Semi-open, and Closed (most efficient, clear liquids only).

• Maintenance Troubleshooting:   - No delivery: Loss of prime, head too high, or plugged impeller.   - Insufficient Pressure: Speed too low, air leaks, or mechanical defects.   - Excessive Power Draw: Packing too tight, bent shaft, or pumping fluid that is too thick.   - Reverse Rotation: Never run in reverse; may unthread the impeller.

• Valves and Sealing: Sealing fluid must be delivered at a pressure higher than the pump suction pressure. Lantern rings/Lantern plates are used for injection sealing.