Filter, relief and solenoid valves

Hydraulics → Advanced · schematic symbols, physical flow laws and dimensionless controls.

Filter with bypass

Two hydraulic ports: IN and OUT. The diamond represents the filter medium; the parallel spring-loaded check valve bypasses it when the inlet-to-outlet differential exceeds the cracking pressure.

Δp = pIN − pOUT
Q_filter = Δp / R_filter
Q_bypass = max(Δp − p_bypass, 0) / R_bypass
QIN = Q_filter + Q_bypass; QOUT = −QIN

Defaults: R_filter = 10⁹ Pa·s/m³, p_bypass = 200000 Pa, R_bypass = 10⁸ Pa·s/m³. Both resistances must be positive; the cracking pressure may be zero. Reverse flow passes through the medium, with the bypass closed.

Enable Expose bypass status output (0/1) in Properties to show the pink bypass port. Disabling it removes its outgoing signal connections. The bypass valve itself always operates. The bypass result remains available in charts and CSV even when the connector is hidden.

The internal bond graph has inlet/outlet 0-junctions and two parallel branches, each with a 1-junction and a one-port resistance. Increase the fixed filter resistance to represent contamination; this block does not integrate a clogging state.

Pressure relief valve

Connect P to the pressure line and T to the return. The direct-acting spring-loaded symbol indicates pressure relief from P to T. Return backpressure affects the opening threshold.

Δp = pP − pT
QP = max(Δp − p_set, 0) / R_open; QT = −QP
relief = 1 when open, otherwise 0

Defaults: p_set = 10⁷ Pa, R_open = 10⁸ Pa·s/m³. The setting must be nonnegative and resistance positive. The finite resistance models pressure override: carrying Q requires Δp = p_set + Q·R_open. This is not an ideal pressure clamp.

The pink relief output is dimensionless and may be left unconnected. Internal graph: a common-flow 1-junction and a nonlinear one-port R. Reverse flow and closed leakage are zero.

2/2 solenoid valve

Two ports (P, A), two discrete positions. The solenoid on the left actuates the open position; the spring on the right returns the valve to its normally closed position. Connect a dimensionless source or status output to u.

u = 0: QP = QA = 0
u = 1: QP = (pP − pA) / R_open; QA = −QP

Default R_open = 10⁸ Pa·s/m³, strictly positive. Open flow is bidirectional. The input accepts exactly numeric 0 or 1; fractional values and nonconstant linear ramps are rejected. Use Boolean Schedule for timed switching. The signal input is required for analysis.

Internal graph: a 1-junction and a switched resistance. Both power ports remain required when closed; each isolated side still needs a determined pressure.

Status outputs and example

Both status outputs are numeric 0/1 (unit 1), with step interpolation. A status is 1 above its cracking pressure and 0 at or below it; a relative 10⁻¹⁰ pressure tolerance suppresses numerical roundoff at the threshold. This is not physical hysteresis. One output may drive multiple inputs; an input accepts one driver.

Connected status signals are solved simultaneously with the hydraulic network, with no one-step delay. Up to eight distinct status outputs may drive controls. Instantaneous feedback with multiple consistent modes or no consistent mode is rejected with a diagnostic. All three components are ideal, without switching delay, hysteresis, inertia or stored energy. Dissipation is Δp·Q ≥ 0.

Open Hydraulics: filter bypass, relief and solenoid. At 1 s the filter differential rises from 100000 to 300000 Pa, opening its 200000 Pa bypass and energizing the separate solenoid circuit. At 2 s the relief circuit rises from 200000 to 500000 Pa, exceeding its 300000 Pa setting. The independent branches make status behavior easy to inspect. Parameters are illustrative.

Results include pressure drop, total flow, dissipated power, filter/bypass branch flows, status and applied control. Save/Open preserves parameters, optional output visibility, signal connections and rotation.

Symbol reference: Hidraoil hydraulic symbols. The drawings are adapted to the editor's named ports.