Engineering Selection Tools

Input parameters

Action type

Bore diameter mm

Rod diameter mm

Gauge pressure bar

Stroke mm

Cycles per minute c/min

Results

Effective extension force

—

N · includes baseline 0.85 efficiency factor

Effective retraction force

—

N · rod-side area for double acting cylinders

Free air consumption

—

Nl/min · approximate, based on absolute pressure

Rod / bore ratio check

—

Not included

spring force on single acting cylinders
pressure losses, cushioning and valve flow limits
buckling, side loads and mounting constraints
supplier-specific safety factors

Input parameters

Load mass kg

Friction coefficient µ

Linear guide often 0.002–0.01 · sliding contact may be higher

Target velocity mm/s

Acceleration m/s²

Axis orientation

Transmission efficiency η

Design factor

Results

Acceleration force

—

N

Peak linear force

—

N · friction + gravity + acceleration

Design linear force

—

N · includes design factor

Baseline mechanical power

—

W · includes transmission efficiency and design factor

Selection note

Motor sizing still requires torque-speed curve, duty cycle, reflected inertia, transmission ratio, drive voltage, thermal limits and peak/RMS torque verification.

Not included

moving actuator mass and payload inertia
ballscrew, belt or gearbox ratio
motion profile shape and dwell time
servo drive limits and thermal derating

Input parameters

Bore diameter mm

Rod diameter mm

Operating pressure bar

Rod velocity mm/s

Hydraulic efficiency η

Results

Push force

—

kN · cap-end area

Pull force

—

kN · annular rod-side area

Required flow rate

—

l/min · push direction

Hydraulic power

—

kW · adjusted for efficiency

Not included

pressure drops through valves, hoses and manifolds
buckling, column strength and end fixing
fluid temperature, leakage and duty cycle
shock loads and decompression effects

Input parameters

Axial load N

Lead mm/rev

Required linear velocity mm/s

Screw efficiency η

Ball screw often 0.85–0.95 · sliding screw may be much lower

Design factor

Results

Required rotational speed

—

rpm

Running torque

—

Nm · before acceleration/inertia

Design torque

—

Nm · includes design factor

Required power

—

W · based on axial force and linear speed

Back-driving note

—

Not included

critical speed and screw whip
buckling, bearing arrangement and unsupported length
nut life, lubrication and duty cycle
rotary inertia and acceleration torque

Input parameters

Actuator bore diameter mm

Rod velocity mm/s

Number of simultaneous actuators

System pressure bar

Overall system efficiency η

Gear pump ~0.80–0.88 · Piston pump ~0.88–0.94

Design factor

Results

Required flow rate

—

l/min · cap-end, all actuators combined

Design flow rate

—

l/min · includes design factor

Hydraulic power

—

kW · pressure × flow

Required shaft power

—

kW · adjusted for system efficiency

Not included

return line back-pressure and standby losses
heat rejection, fluid cooling requirements
reservoir sizing and fluid volume
pump displacement selection and speed range

Input parameters

Pipe / hose internal diameter mm

Line length m

Flow rate l/min

Fluid type

Operating temperature °C

Viscosity is corrected for temperature (Walther equation)

Equivalent fittings length factor ×L

1.0 = straight pipe only · 1.3 typical with elbows and tees

Results

Flow velocity

—

m/s · at operating conditions

Reynolds number

—

Pressure drop

—

bar · Darcy-Weisbach, corrected viscosity

Velocity check

—

Not included

individual fitting pressure losses (Kv method)
pipe roughness effects above ~Re 4000
fluid compressibility and aeration
filter, valve and manifold pressure drops

Input parameters

Calculation mode

Flow rate l/min

Valve Kv value m³/h at 1 bar

Pressure drop across valve bar

Fluid density ρ kg/m³

Mineral oil ~860–880 · Water 1000 · HF-E ~1060

Upstream pressure p1 bar

Used for cavitation index only

Results

Kv required

—

m³/h at 1 bar ΔP

Cv equivalent

—

US gpm at 1 psi ΔP · Cv = Kv × 1.156

Cavitation index (σ)

—

Cavitation risk

—

Not included

gas / two-phase flow correction factors
choked flow and flashing conditions
valve authority and control stability
noise, erosion and seat velocity limits

Input parameters

Accumulator function

Required usable volume l

Volume to deliver between p1 and p2

Minimum working pressure p1 bar

Maximum working pressure p2 bar

Process type

Pre-charge safety margin

Pre-charge p0 = p1 × margin · typically 0.85–0.92

Results

Pre-charge pressure p0

—

bar · nitrogen gas charge at ambient temperature

Required total gas volume

—

l · at pre-charge state (bladder fully extended)

Recommended accumulator size

—

l nominal · nearest standard size above calculated volume

Pressure ratio check (p2/p0)

—

Not included

temperature correction on gas pre-charge
bladder / piston fatigue life and cycle rating
manifold, safety block and dump valve sizing
pressure vessel certification and safety factors

Input parameters

Servo / stepper axes count

Each axis: 2 DI (enable/fault) + 2 DO (enable/reset) + 1 AI (current feedback)

Discrete sensors (prox, photo, limit) count

Solenoid valves / discrete outputs count

Analog sensors (pressure, temp, pos) count

Analog outputs (proportional valves, VFDs) count

Safety I/O — E-stops, guards, door locks count

Safety DI counted as dual-channel pairs

I/O spare margin %

Results

Digital inputs (DI)

—

channels incl. spare

Digital outputs (DO)

—

channels incl. spare

Analog inputs (AI)

—

channels incl. spare

Analog outputs (AO)

—

channels incl. spare

Safety I/O channels

—

dual-channel DI pairs · dedicated safety module required

Estimated I/O modules

—

16-ch DI/DO + 8-ch AI/AO baseline — verify with rack layout

Not included

HMI, SCADA and historian connections
fieldbus node addressing and topology
power supply sizing and cabinet layout
PLC CPU scan time and memory requirements

Input parameters

Load inertia J_load kg·m²

Motor rotor inertia J_motor kg·m²

From motor datasheet · inertia ratio J_load/J_motor check

Peak angular acceleration rad/s²

Continuous load torque T_load Nm

Maximum speed rpm

Drive / transmission efficiency η

Design factor

Results

Peak acceleration torque

—

Nm · (J_load + J_motor) × α

Peak motor torque required

—

Nm · includes load torque, acceleration and design factor

Continuous motor power

—

W · at maximum speed, adjusted for efficiency

Inertia ratio J_load / J_motor

—

Inertia matching check

—

Not included

motion profile shape — trapezoidal vs S-curve
RMS torque over full duty cycle
gearbox ratio optimisation
drive DC bus sizing and regeneration

Input parameters

Fieldbus protocol

Number of nodes / slaves count

Process data per node bytes

Typical drive PDO: 4–8 bytes · I/O node: 2–4 bytes

Target application cycle time µs

Results

Estimated minimum cycle time

—

µs · based on frame overhead + propagation

Total bus utilisation

—

% of available bandwidth at target cycle

Maximum nodes at target cycle

—

nodes before cycle time is exceeded

Cycle time feasibility

—

Not included

switch latency and topology delays (star vs line)
jitter, synchronisation accuracy and drift
cable propagation delay beyond 100m segments
master CPU processing time and stack overhead

Input parameters

Safety function architecture

Component failure rate λ_D failures/h

Typical SIL-rated relay: 1×10⁻⁷ · PLC I/O: 1×10⁻⁶ · Standard sensor: 1×10⁻⁵

Diagnostic coverage (DC) %

No DC: 0% · Low: 60% · Medium: 90% · High: 99%

Proof test interval T₁ years

Common cause failure β %

IEC 62061 Table D.5: typically 1–5% for well-separated channels

Results

PFD_avg — probability of failure on demand

—

average over proof test interval

Achieved SIL level

—

per IEC 62061 / IEC 61508 PFD bands

Risk reduction factor (RRF)

—

RRF = 1 / PFD_avg

SIL claim check

—

Not included

hardware fault tolerance (HFT) verification
safe failure fraction (SFF) calculation
systematic capability and software SIL
full IEC 61508 / ISO 13849 functional safety assessment

Engineering selection tools.

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What these tools establish

What context adds

Turn the baseline into a selection decision.