Hydraulic Solenoid Valve Connectors: Comparing 5 Wiring Types, IP Ratings and Selection Criteria

The connector is the electrical interface between your control signal and the solenoid coil. The same valve installed on an outdoor mobile machine and in a dry cleanroom production line calls for two very different connectors. This guide compares the five connector types offered by TAI-HUEI — LW Terminal Box, DL DIN Plug, M4 Pin Type Fast Connector, 2W Two Wires and DT Deutsch Connector — by ingress protection rating, mounting method and operating environment, so you can match the wiring solution to the conditions your equipment actually sees.

In practice, the reliability of a solenoid directional valve depends on far more than the machining accuracy of the valve body. The choice of connector is often what determines whether a machine runs continuously for years or trips a production line. Where the connector design or IP rating does not match site conditions, coolant ingress, metallic dust build-up and vibration-induced loose contacts follow — and an entire automated line can be forced to stop.

TAI-HUEI has more than 50 years of experience developing and manufacturing hydraulic valves. Our G02/D03 (1/4" / NG6) and G03/D05 (3/8" / NG10) Solenoid Directional Valve series are available with five connector types — LW, DL, DT, M4 and 2W — covering a wide range of mounting arrangements, wiring requirements and operating environments. The sections below outline the characteristics, typical applications and selection considerations for each.

The five TAI-HUEI connector types

Five standard wiring types are available, each suited to a different combination of environment and installation constraint.

DL — DIN Plug Type

The DL connector is built to the DIN 43650 Form A international standard and incorporates an LED that indicates coil energization in real time. A screw-retained design gives a secure mount with straightforward installation and removal, and the assembly achieves IP65 protection.

Technical features.

When the coil is energized, the integrated LED illuminates. Maintenance staff can confirm at a glance whether the coil has received its control signal. When a fault occurs there is no need to reach for a multimeter first — the indicator alone shows whether the PLC output is present, which cuts fault-finding time considerably.

Pin assignment.

The standard configuration is a 3-pin connector. Pins 1 and 2 are the supply terminals (AC coils are normally non-polarized; DC coils must be wired to the correct polarity). Pin 3, or a separate terminal, is the protective earth (PE) connection.

Points to note.

DL connectors use different indicator circuits for AC and DC coils. AC versions normally include a rectifier, while DC versions require attention to polarity and to the orientation of any protective components such as flyback diodes. Specifying the wrong version, or wiring it incorrectly, may prevent the LED from illuminating or damage the indicator circuit. Confirm coil voltage, supply type (AC or DC) and connector specification before ordering.

LW — Terminal Box Type

The LW connector uses a single central terminal box with internal terminal-block wiring and a built-in surge suppressor. The generous internal volume accepts larger cable cross-sections and improves both wiring convenience and electrical protection.

Technical features.

The box provides ample room to work, accommodating heavier-gauge cable terminated on screw terminals. The result is a secure, maintainable connection well suited to large conductor sizes and long cable runs.

Circuit protection.

De-energizing a solenoid coil generates a reverse voltage transient. The varistor fitted inside the terminal box absorbs this surge, reducing stress on PLC output modules, relays and other control components, and extending the service life of the control system.

M4 — M12-4Pin Type Fast Connector (M12-4PIN)

The M4 connector uses a standard M12 4-pin circular format, consolidating the control signals for both coils of a double-solenoid valve into a single outlet. A metal threaded coupling provides good sealing, vibration resistance and connection stability. Once the machine is wired, servicing requires no re-stripping of conductors or disturbing of terminals — the connector simply unscrews, allowing a rapid valve change with far less risk of wiring error.

Technical features.

The standard M12 4-pin format is keyed against mis-mating and accepts off-the-shelf M12 cordsets, so no field crimping or rewiring is required.

Pin assignment.

Pin 1 — common (COM).

Pin 2 — solenoid A control signal.

Pin 3 — reserved / not used.

Pin 4 — solenoid B control signal.

Application advantages.

The connector interfaces directly with PLCs, distributed I/O modules and IO-Link systems, reducing field wiring complexity and supporting a more modular machine architecture.

2W — Two Wires Type

The 2W connector uses a high-protection direct-exit design: two insulated conductors emerge from the coil body itself, potted in a single high-temperature resin molding. Eliminating the external plug and terminal box saves installation space. The assembly achieves IP67, giving effective protection against dust ingress and short-term immersion.

Technical features.

Because the conductors and coil are potted as one piece and sealed at the exit point, the number of external connectors and contact points is reduced — lowering the risk of failure from moisture, oil contamination or intermittent contact, while saving space.

Application advantages.

Well suited to hydraulic power units (HPUs), control cabinets and other space-constrained installations. The leads can run straight to a terminal strip inside the cabinet, reducing the number of wiring interfaces and improving overall reliability.

DT — Deutsch Connector Type

The DT connector uses the Deutsch DT04-2P format, with twin-rail contacts, a high-density O-ring, sealing gaskets and a rubber boot for excellent sealing, weather resistance and vibration tolerance. A latching quick-connect design allows fast installation and removal, and the assembly achieves IP68.

Technical features.

Multiple sealing barriers keep out moisture, oil and dust, reducing contact oxidation and intermittent connection. Electrical performance remains stable even under prolonged outdoor exposure or regular high-pressure washdown.

Application advantages.

The IP68 rating improves reliability where mud, spray, humidity and dust are present, reducing the risk of contact oxidation and signal faults caused by water ingress and contamination. The latching mechanism also reduces the chance of the connector working loose under vibration.

Click to View TaiHuei Hydraulic Solenoid Valve Coil Protection Rating Certification Reports

Application guidance and connector selection

Start by assessing the operating environment, then select the corresponding IP rating and connector format.

DL DIN Plug Type (IP65)

Suitable for general industrial environments, the built-in LED provides a visual indication of coil energization, enabling quick verification of the control signal and reducing troubleshooting time. Ideal for machine tools, automation equipment, and injection molding machines.

LW Terminal Box Type

Ideal for heavy machinery, medium- to large-scale hydraulic systems, and equipment requiring continuous operation. The junction box design offers flexible wiring, easy maintenance, and ample internal space for future wiring modifications or the installation of protective devices such as surge suppressors.

M4 M12-4Pin Type Fast Connector (M12-4PIN)

Suitable for automated production lines requiring frequent maintenance, tool changes, or valve replacement. The threaded coupling nut allows quick installation and removal, enabling valve replacement within seconds. It integrates seamlessly with distributed I/O and IO-Link systems, making it ideal for semiconductor equipment, automated material handling systems, and lithium battery manufacturing lines.

2W Two Wires Type (IP67)

Suitable for densely arranged valve assemblies and space-constrained installations, including hydraulic power units, compact control cabinets, and outdoor equipment. The 2W connector is an excellent choice for applications requiring long-term operation in damp, dusty, or high-vibration environments where simplified wiring and compact installation are essential.

DT Deutsch Connector Type(IP68)

Designed for demanding outdoor, high-humidity, high-vibration, and mud-spray environments, the DT connector is widely specified for construction machinery, excavators, port cranes, agricultural machinery, and vehicle-mounted hydraulic systems. Its superior sealing performance and vibration resistance help minimize the risk of intermittent contact, wiring failures, and signal interruptions.

Choosing the right connector for your machine

No connector type is inherently better than another. What matters is the fit with your equipment, operating environment and maintenance strategy.

Step 1 — Define the operating environment.

Establish whether the equipment runs indoors or outdoors, and whether moisture, oil, dust, coolant or heavy vibration are present.

Step 2 — Select the IP rating.

Determine the dust and water protection the site actually requires, and set the IP rating accordingly.

Step 3 — Assess maintenance frequency.

Consider your servicing and replacement requirements, and whether quick-disconnect, energization indication or other maintenance-oriented features are worth having.

Step 4 — Confirm wiring and installation space.

Finally, review the control cabinet, manifold and surrounding clearances, and choose the connector that best matches your wiring method and mounting constraints.

If you are unsure which connector best suits your installation, contact the TAI-HUEI engineering team directly. We will provide specific selection guidance and a complete hydraulic control solution for your application.

Not sure which connector type is right for your application?Contact TaiHuei's hydraulic experts today.

We provide professional selection recommendations and customized hydraulic control solutions to ensure optimal performance for your equipment.

Coil selection — frequently asked questions

Q: Why do connector type and IP rating have such a direct effect on machine reliability?

The solenoid directional valve is the core energy-conversion element in a hydraulic control system, directing oil flow to drive cylinders and motors. Most factory environments carry atomized coolant mist, hot water vapor or metallic dust. Where the connector’s IP rating is inadequate, these particles work through the joints and into the contacts, causing oxidation, rising contact resistance and — in the worst case — a short circuit that burns out the coil. Specifying the right connector materially reduces the hidden cost of unplanned downtime.

Q: Is there a real case where the wrong connector caused a line stoppage?

Yes. A major Taiwanese machine tool manufacturer relocated a hydraulic valve stack to a position beneath the machining tank, where it was exposed to heavy coolant spray, following a customer-driven design change. The machine had been built entirely with DL DIN Plug Type connectors (IP65). Although splash-resistant, under prolonged saturation by high-concentration coolant and vapor ingress the connectors repeatedly admitted water within six months, leaving the coils unable to actuate properly. The fault was initially misdiagnosed as contamination jamming the valve body, and several valves were replaced without resolving anything.

After a TAI-HUEI engineer visited the site, the root cause was confirmed as insufficient ingress protection. On our recommendation, the installation was converted throughout to DT Deutsch Connector Type with IP68 sealing. Since the changeover, the same valves have operated reliably in the same aggressive coolant environment, with no further water-ingress stoppages.

Q: How does water resistance differ between the DL, 2W and DT connectors?

The main differences are the IP rating and the sealing architecture. DL DIN Plug Type (IP65) protects against dust and low-pressure water jets, with a built-in LED confirming coil energization. 2W Two Wires Type (IP67) has conductors and coil potted as one piece, reducing external connections and the risk of water ingress. DT Deutsch Connector Type (IP68) withstands prolonged immersion, with excellent sealing and vibration resistance.

Q: Why are more smart automation builders specifying the M4 Pin Type Fast Connector (M12-4PIN)?

Because M12 4-pin is the common standard interface for Industry 4.0 and modular machine design, and it offers quick disconnection, keyed mating and vibration resistance.

With conventional wiring, replacing a valve means stripping conductors, crimping terminals and landing them on a terminal block against a wiring diagram — slow work with plenty of scope for error. The M4 connector is keyed: swapping a valve means unscrewing the metal coupling nut, fitting the new valve and tightening again, cutting replacement time by more than 80%. It also mates directly with distributed I/O modules, aligning well with modular production and rapid commissioning.

Q: Which connector is recommended when manifold space is tight?

The 2W Two Wires Type connector. Compared with the DL or LW types, which have external connector bodies, the 2W removes protruding hardware and avoids interference with adjacent components — making it particularly suitable for enclosed hydraulic power units (HPUs), compact control cabinets and space-constrained equipment. Its IP67 rating provides both dust and water protection, improving reliability in damp, dusty environments.

Connector selection is about lifecycle cost, not unit price

Early in a machine design, connector cost tends to be treated as a minor line item. For industrial equipment running continuously, however, it is maintenance time, downtime losses and fault-finding efficiency that drive total cost of ownership (TCO).

For example: on automated equipment requiring frequent tool changes, valve swaps or rapid repair, the M4 Pin Type Fast Connector (M12-4PIN) or DT Deutsch Connector Type shortens replacement time through quick-disconnect design and removes the error risk associated with rewiring. The LW Terminal Box Type and DL DIN Plug Type, meanwhile, suit fixed installations that need wiring flexibility or quick confirmation of coil status respectively.

Connector selection should therefore not come down to purchase price alone, but to a combined assessment of operating environment, maintenance frequency and the cost of downtime. On lines where a stoppage is expensive, spending a little more on the connector to reduce repair time and failure risk usually delivers a better return over the life of the equipment.

Written by the Hydraulic Systems Application Engineering Team, TAI-HUEI Hydraulic. Last updated: July 2026.

References and Applicable Standards

The connector types and protection rating definitions described in this article are based on the following international standards. Actual product specifications shall be subject to TaiHuei Hydraulic product catalogs and certification reports.

IEC 60529 — Degrees of protection provided by enclosures (IP Code), Edition 2.2 (2013)
The definitions of IP65, IP67, and IP68 in this article are based on this standard. The first digit indicates protection against solid particles (dust), and the second digit indicates protection against water ingress.

DIN EN 175301-803 — Rectangular connectors for solenoid valves (formerly DIN 43650)
Form A connectors feature an 18 mm pin spacing. The DL LED indicator connector described in this article complies with this specification.

IEC 61076-2-101 — Circular connectors, M12 threaded locking connectors
The M4 (M12 4-Pin) quick connector described in this article is based on this standard.

TaiHuei Hydraulic Industrial Co., Ltd. solenoid valve coil protection rating certification reports and product catalogs.

Verification Date: July 28, 2026
Standards and specifications are subject to revision. In case of updates, the latest information published by the issuing organizations shall prevail.