1. Overview

The Индикатор момента нагрузки (LMI, also called a moment limiter) and the Onboard Weighing System are critical devices that keep excavators, loaders, truck cranes and other hydraulic engineering machines operating safely and efficiently. seezol Technology’s measurement principle is to install oil pressure sensors on the hydraulic circuit to capture cylinder working pressure in real time, then convert it — through a calibrated algorithm — into the current load mass and resultant moment, enabling overload warning and limiting.

SeeZol oil pressure sensors ship with a unified 1/4-inch interface. This standardization means the field work is reduced to bridging the sensor’s 1/4 end to the machine’s hydraulic end, which greatly simplifies model selection and spare-parts management.

2. Three Installation Methods by Hydraulic Line Connection Type

Depending on how the machine’s hydraulic lines are joined, field installation of the oil pressure sensor falls into three categories.

2.1 Tee-Joint Installation (threaded connection machines)

Applies to: machines whose hydraulic pipes connect by threaded butt joints.

Принцип: A tee fitting is added at the original threaded joint, paralleling the oil pressure sensor into the circuit for pressure sampling without interrupting the main flow.

Steps:

1. Measure the original joint thread. This is the most critical step — accurately measure the specification of both original threads (metric M, BSP/G, NPT, etc., with exact dimensions) and select a tee whose top and bottom ends match exactly.

1. Handle the side port. The tee’s side port can either take an adapted 1/4 adapter to connect the oil pressure sensor directly, or be welded with the 1/4 elbow connector supplied by seezol before the sensor is screwed in.

Примечание: Thread selection must be based on measurement; wrong selection causes seal failure.

2.2 Flange Installation (clamp / quick-coupler machines)

Applies to: machines whose hydraulic pipes connect by clamp (quick coupler) joints.

Принцип: A dedicated flange is added at the clamp joint; the flange side carries a reserved 1/4 sensor port.

Steps:

1. Measure the center-to-center spacing of the clamp’s four bolts and confirm the bolt thread size.

1. Select or custom-make a matching flange from the measured data; its side carries a built-in 1/4 port for the oil pressure sensor.

Примечание: This method does not alter the clamp’s original seal structure — it only fixes the flange via the clamp’s bolt holes, giving a stable mount that is also easy to remove for maintenance.

2.3 Explosion-Proof Valve Installation (machines with burst valves)

Applies to: machines whose hydraulic lines are equipped with an explosion-proof valve (also called a burst valve or balance valve).

Принцип: The explosion-proof valve normally reserves a main pressure-test port; the oil pressure sensor screws straight in, with no complex adapter needed.

Steps:

1. Locate the valve’s main pressure-test port.

1. If the port is a standard 1/4 interface, screw the oil pressure sensor in directly.

1. If the port is non-standard, add a 1/4 adapter interface first, then connect the sensor.

Примечание: This is the simplest method, and because the test point is the system’s true pressure point, signal quality and response are excellent.

3. Mandatory Rule: Connector Dimensions Must Match Exactly

Whatever method is used, the first iron rule is: all connector dimensions must match exactly. A hydraulic line is a high-pressure sealed system, and any dimensional deviation must never be force-installed. Even a hairline mismatch force-threaded in leaves the threads under-engaged, breaking the seal and causing oil seepage. Seepage not only distorts the pressure sample and ruins measurement accuracy, it can also spray under high pressure and create a safety hazard; meanwhile force installation easily damages the machine’s original fittings, leading to costly repairs. Therefore, whenever dimensions are in doubt, always follow the sequence: measure first, select second, install last.

4. Sensor Position and Orientation

Position and orientation are based on ease of oil-pressure signal-cable routing, following these principles:

• Prefer inner-end mounting — place the sensor on the inner side of the structure to reduce exposure to impact.

• Fully assess the working range of the boom (arm) during operation; ensure that neither the machine body nor external obstacles can scrape the sensor or cable in any posture.

• Orient the sensor to favor cable exit, avoiding wrap-around by rotating or extending parts.

5. Signal Cable Protection and Routing

Job sites are harsh and cables are easily damaged; protect them as follows:

• Run the signal cable inside corrugated conduit throughout to resist abrasion, oil and impact.

• Route along the machine’s own hydraulic hoses, using existing channels and fixing points — neat and less likely to come loose.

• Leave appropriate slack so that boom lifting/lowering, which stretches the hoses, does not pull the signal cable tight or snap it.

6. Limitations and Additional Notes

• This guide is compiled from seezol Technology’s audit conclusions on typical models; special models or modified vehicles should be evaluated against their actual hydraulic circuits.

• After occupying the explosion-proof valve’s main test port, confirm it does not affect the valve’s original balancing and locking function.

• After installation, perform a pressure-hold and leak check before putting the load-measurement system into service.

7. Disclaimer

This technical guide is compiled by seezol Technology for reference by installation and maintenance personnel only. Installing pressure sensors involves high-pressure hydraulic systems; improper operation may cause personal injury or equipment loss. Actual work must be carried out by qualified personnel, strictly following the corresponding machine’s service manual and relevant safety standards. seezol Technology is not directly liable for any consequences arising from non-compliant operation.