Pressure Switch Wiring in Hydraulic Roll Forming Systems (Electrical Integration Guide)

Pressure Switch Wiring in Hydraulic Systems

Electrical Integration for Roll Forming & Coil Processing Machines

Pressure switches are critical in hydraulic-powered roll forming machines.

They are used to:

• Confirm hydraulic system pressure before cut

• Verify punch cycle completion

• Prevent dry running of pumps

• Detect overpressure conditions

• Provide safety interlock feedback

• Monitor accumulator pressure

Incorrect wiring or configuration causes:

• Shear misfires

• Punch incomplete strokes

• Hydraulic pump overload

• Nuisance trips

• Safety non-compliance

• Component damage

In roll forming systems where flying shears and punches rely on hydraulic force, pressure switch integration must be engineered with both electrical and mechanical precision.

This guide explains how to properly wire, protect, and integrate hydraulic pressure switches in industrial roll forming machines.

1) What Is a Hydraulic Pressure Switch?

A pressure switch:

• Monitors system pressure

• Activates electrical contact at preset pressure

• Provides ON/OFF signal

It is not an analog sensor (unless specifically pressure transmitter).

It is a discrete switching device.

Most common configuration:

• Normally Open (NO)

• Normally Closed (NC)

• SPDT (Single Pole Double Throw)

2) Typical Use Cases in Roll Forming

Flying Shear:

Pressure must reach threshold before blade movement allowed.

Punch Press:

Pressure confirmation ensures full force achieved.

Hydraulic Pump Protection:

Low pressure detection stops pump to prevent damage.

Accumulator Systems:

Confirms pressure within operating range.

3) Basic 2-Wire Pressure Switch Wiring (Fail-Safe Design)

Most industrial setups use 24VDC control.

Word-Based Wiring:

24VDC →
Pressure Switch COM

Pressure Switch NC →
PLC Digital Input

PLC Input Common → 0V

When pressure normal:

Circuit closed → PLC input ON.

If pressure lost or wire breaks:

Circuit opens → PLC input OFF → machine stops.

NC preferred for safety-critical pressure confirmation.

4) 3-Wire Pressure Switch (With Signal + Power)

Some electronic pressure switches use:

• Brown → +24V
• Blue → 0V
• Black → Signal Output

Wired similarly to proximity sensors.

Black → PLC Input.

Confirm output type:

PNP or NPN.

5) Word-Based Integration – Flying Shear Pressure Confirmation

• Hydraulic Pump ON →
• Pressure Builds →
• Pressure Switch Activates →
• PLC Input ON →
• PLC Enables Shear Cycle

If pressure not achieved:

PLC blocks shear command.

Prevents incomplete cut stroke.

6) Overpressure Protection Circuit (Safety Layer)

Word-Based:

• 24VDC →
• Overpressure Switch (NC) →
• Safety Relay →
• Main Contactor Coil

If pressure exceeds limit:

Switch opens → Safety relay drops → Hydraulic system disabled.

Critical in high-tonnage systems.

7) Electrical Noise & Hydraulic Solenoids

Hydraulic systems generate electrical noise from:

• Solenoid valves

• Pump motor switching

• VFD drives

Pressure switch wiring must:

• Be routed away from motor cables

• Use shielded cable for long runs

• Avoid parallel runs with VFD output

Noise can cause false pressure signal.

8) Switch Adjustment & Calibration

Pressure switch has adjustable setpoint.

Improper calibration causes:

• Shear firing too early

• Punch under-force

• Pump cycling frequently

• Overpressure damage

Electrical system must match mechanical pressure setting.

Always calibrate under load.

9) Contact Rating & Current Considerations

Pressure switches usually low-current control devices.

Never wire directly to:

• High-current coil without relay

• AC motor circuit

Use interposing relay if needed.

Protect contacts from arcing.

10) Suppression for Relay & Solenoid Loads

If pressure switch drives a relay:

Install suppression diode (DC) or RC snubber (AC).

Word-Based:

Relay Coil → Diode across terminals.

Prevents contact damage.

Without suppression:

Switch contacts burn prematurely.

11) PLC Logic Integration

Typical PLC logic:

• IF Pressure_OK = TRUE
• AND Strip_Present = TRUE
• AND Home_Position = TRUE
• THEN Enable_Cut

Pressure signal often one of multiple safety conditions.

12) Common Wiring Mistakes

1. Using NO contact for safety circuit

2. Wiring directly to high-current coil

3. Incorrect PNP/NPN matching

4. No suppression diode

5. Poor grounding

6. Long unshielded cable near VFD

7. Incorrect setpoint adjustment

8. Ignoring pressure hysteresis

Many hydraulic “mechanical” problems are actually electrical signal errors.

13) Voltage Stability & Control Power

Pressure switches rely on stable 24VDC.

Voltage sag causes:

• False drop-out

• Random machine stop

• PLC input flicker

Use:

• Separate control transformer

• Proper power supply sizing

14) Testing & Commissioning Procedure

1. Verify wiring configuration

2. Confirm correct NO/NC contact

3. Measure pressure at activation

4. Verify PLC input state change

5. Simulate pressure loss

6. Confirm safety response

7. Inspect cable routing

8. Document setpoint value

Test at full production pressure.

15) Mechanical Placement Considerations

Pressure switch must be installed:

• On stable pressure point

• Away from pulsation spikes

• After pump but before main valve block

Incorrect placement causes unstable signal.

Use damped port if needed.

16) Export & Service Considerations

When exporting roll forming machines:

• Confirm voltage rating

• Provide wiring diagram

• Document setpoint value

• Label terminal clearly

• Include spare pressure switch

Wrong replacement rating common in overseas service.

17) Failure Modes in Roll Forming

Common pressure switch faults:

• Contact wear

• Internal diaphragm fatigue

• Loose wiring terminal

• Oil contamination

• Incorrect re-adjustment

• Wire break at vibration point

Periodic inspection required.

18) Buyer Strategy (30%)

Before purchasing a roll forming machine with hydraulic system, verify:

1. Pressure switch wired in fail-safe NC configuration

2. 24VDC control standard used

3. Suppression installed on relay coils

4. Proper cable routing

5. Pressure setpoint documented

6. Overpressure safety interlock installed

7. PLC logic includes pressure confirmation

8. Commissioning test performed at full load

Red flag:

“Pressure switch bypassed to prevent nuisance trips.”

That indicates unresolved hydraulic or wiring issue.

6 Frequently Asked Questions

1) Should pressure switch be NO or NC?

NC preferred for fail-safe safety circuits.

2) Why does shear fire without enough pressure?

Switch setpoint too low or wiring incorrect.

3) Why does machine stop randomly?

Possible loose wiring or voltage instability.

4) Can I wire pressure switch directly to motor?

No, use relay or PLC input.

5) Why does pressure switch burn out?

Likely no suppression diode on relay coil.

6) What is most common mistake?

Using NO contact in safety loop.

Final Engineering Summary

Pressure switch wiring in hydraulic roll forming systems must ensure:

• Fail-safe NC configuration

• Proper PLC integration

• Suppression of inductive loads

• Stable 24VDC supply

• Correct setpoint calibration

• Shielded cable routing if required

• Safety interlock integration

• Commissioning under full load

Improper integration leads to:

• Shear misfires

• Hydraulic damage

• Pump overload

• Production downtime

In roll forming machines, pressure switches are small devices — but they form a critical link between hydraulic force and electrical control reliability.