Practical Hydraulic Pump Testing Methods and Inspection Procedures to Help Prevent Failures on the Jobsite

When operating construction equipment, it is not uncommon to encounter hydraulic system problems or breakdowns and be unsure how to handle repairs or maintenance.
If the machine continues operating in that condition, a sudden shutdown can lead to major losses.
To prevent trouble before it occurs, regular diagnostics and accurate performance data are essential.

This article explains practical hydraulic pump testing methods and inspection procedures that help prevent failures on the jobsite.
Use it as a guide to accurate measurement procedures and the proper steps for replacing parts with genuine components so you can extend the service life of your construction equipment.

Why Hydraulic Pump Testing Is Necessary

To keep construction equipment operating reliably, hydraulic pump testing should be carried out regularly so abnormalities can be detected early.
The hydraulic system is the core of the machine’s power transmission, and even a minor problem can directly reduce overall performance.

To explain why testing is important, we will look at the following two points.

• Problems that can occur when measurements are neglected
• Key considerations for hydraulic systems in construction equipment

Regular testing can help prevent major failures.

Problems That Can Occur When Measurements Are Neglected

If hydraulic pump pressure and flow rate are not measured for a long period, internal wear and component deterioration can go unnoticed, increasing the risk of sudden failure.
For example, if the machine continues operating with reduced pressure, it will not be able to generate sufficient force and work efficiency will drop significantly.
If abnormal vibration or unusual noise is left unaddressed, it can seriously damage not only the pump itself but also connected piping and cylinders.

If appropriate action is taken in the early stages of a problem, a simple parts replacement is often enough.
That is why periodic measurement should be built into routine maintenance.

Key Considerations for Hydraulic Systems in Construction Equipment

Because construction equipment operates in harsh environments, the hydraulic system is constantly exposed to outside contamination such as dirt and moisture.
Long periods of continuous operation can also raise hydraulic fluid temperature, reducing viscosity and accelerating wear on components.
For that reason, construction equipment requires stricter temperature control and more rigorous oil leak inspections than ordinary industrial machinery.

An unexpected shutdown on a jobsite can directly lead to project delays and major losses.
In addition to daily visual checks, it is important to monitor actual performance values using specialized equipment and carry out maintenance with the goal of extending the service life of the entire machine.

What to Check Before Testing a Hydraulic Pump

Careful preparation and inspection before measurement are essential if you want accurate hydraulic pump test results.

To carry out the work safely and accurately, make sure you do the following three things.

• Inspect the condition and level of the hydraulic fluid
• Bleed air from the piping
• Ensure safety and visually check for external damage and oil leaks

These checks will help improve the accuracy of the test.

Inspect the Condition and Level of the Hydraulic Fluid

Before performing an accurate test, confirm that the hydraulic fluid is at the specified level and that it is not heavily contaminated or milky.
If the fluid level is too low, the pump may draw in air and accurate pressure measurement will not be possible.
If the fluid appears milky because of water contamination, or if metal particles are mixed into it, the fluid should be replaced and the piping cleaned before testing.

If a test is carried out with contaminated fluid, debris may clog the measuring instrument and damage its sensitive sensors.
Check the condition of the fluid using the tank level gauge and by taking a sample so the system is in the best possible condition before testing.

Bleed Air from the Piping

Before starting the test, bleed any air trapped inside the hydraulic pump and piping.
If air is mixed into the fluid, it will compress when pressure is applied, preventing accurate measurements.
The shock caused by collapsing air bubbles can also damage internal components.

One common procedure is to slightly loosen the valve on the discharge side of the pump and let hydraulic fluid flow out while running the machine at low speed until no more bubbles appear.
Once the bubbles disappear and only fluid is flowing steadily, close the valve and make sure the piping remains full of hydraulic fluid.

Ensure Safety and Visually Check for External Damage and Oil Leaks

Because the test involves high-pressure hydraulic fluid, safety must come first.
Before beginning work, carefully inspect the piping joints and the areas around the cylinders for cracks, seepage, or other visible signs of damage.

If there is already a leak, applying pressure during the test may cause the affected area to burst and spray hot oil onto workers.
If you find loose bolts or deteriorated hoses, replace those parts before connecting the measuring equipment.
Creating a safe work environment is essential not only for preventing accidents but also for preventing pressure loss and ensuring accurate test results.

Specific Testing Procedures Using a Hydraulic Tester

On-site diagnosis is generally performed with a dedicated tester that can measure pressure and flow rate.
A portable tester allows you to narrow down the source of the problem without disassembling the machine.

To carry out the test, follow these three steps.

• Connect the tester to the piping and apply a load
• Measure and record pressure, flow rate, and hydraulic fluid temperature
• Compare the results with the reference values

Following the proper procedure makes it possible to assess the pump’s actual condition.

Connect the Tester to the Piping and Apply a Load

First, stop the engine and relieve pressure in the circuit before connecting the dedicated tester.
Use the test port near the pump outlet as the connection point, and securely tighten the high-pressure hose.
Once everything is connected, start the engine and run it at low speed until the hydraulic fluid reaches the specified temperature, typically around 45 to 55°C.

After the fluid temperature stabilizes, gradually close the load valve built into the tester to intentionally apply a load to the system.
Do not close the valve too quickly, as that could create excessive pressure and damage the piping.
Always operate it carefully while monitoring the pressure gauge.

Measure and Record Pressure, Flow Rate, and Hydraulic Fluid Temperature

While the system is under load, read and record the values at the same time.
First, check whether the pressure reaches the specified value, then measure the flow rate at that pressure using the flow meter.
At the same time, measure the hydraulic fluid temperature with a thermometer.
Because hydraulic pump performance changes depending on oil temperature, it is important to record all three values together.

If you set multiple load levels and record the readings under each condition, you can get a clearer picture of how the pump’s performance changes under load.

Compare the Results with the Reference Values

Do not simply record the readings—compare them carefully with the standard values listed in the machine’s service manual.
If the measured pressure does not reach the specified value, or if the flow rate drops sharply when the specified pressure is applied, there may be an internal problem in the pump.
If the fluid temperature rises faster than normal, abnormal friction may be occurring inside the unit.

By objectively determining how much performance has deteriorated compared with the pump’s condition when new, you can make an accurate diagnosis without relying on intuition alone.
This comparison is the foundation for building the right maintenance plan afterward.

Identifying the Cause of Failure from Hydraulic Pump Test Results

The data obtained from the tester provides reliable clues for identifying the cause of a failure.
Depending on which values are abnormal, it is often possible to narrow down the faulty component and the area that requires repair.

As a practical guide, focus on the following three situations.

• When pressure does not rise
• When flow rate is insufficient
• When both pressure and flow rate are abnormal

Identifying the cause accurately allows you to build a repair plan without unnecessary work.

When Pressure Does Not Rise

If the measured pressure does not reach the specified value, there is a strong possibility of a problem with a valve that controls pressure in the hydraulic circuit.
The relief valve, which is designed to release pressure above the set limit, may be worn or held open by debris, allowing pressure to escape and preventing the machine from producing full force.
It is also possible that the clearances between internal pump components have become too large.

In any case, pressure is leaking away somewhere in the system, so start by cleaning the valve and adjusting its setting.
If that does not solve the problem, consider replacing the internal packings and seals.

When Flow Rate Is Insufficient

If pressure is normal but the flow rate is extremely low, the pump is not drawing in enough oil.
If the suction filter is clogged with dirt or mud, suction resistance increases and the flow rate drops.
It is also not uncommon for air to be drawn in through the suction-side piping.

In some cases, the pistons and cylinder block inside the pump are severely worn, allowing the fluid that should be discharged to leak back internally.
When this happens, the first step is to inspect the suction-line filter and hose connections and make sure there is a smooth, unrestricted flow path for the oil.

When Both Pressure and Flow Rate Are Abnormal

If both pressure and flow rate are below specification, it is a sign that the hydraulic pump itself has reached the end of its service life or that a serious problem has developed elsewhere in the system.
When the pump’s major internal components are worn to their limit, it can no longer generate pressure or deliver hydraulic fluid properly.

There may also be a major leak or blockage somewhere in the piping, or the hydraulic fluid may have deteriorated so badly that it can no longer perform its intended function.
When the system reaches this condition, replacing only a few parts is often not enough.

What to Do After Testing and How to Replace Parts Correctly with Genuine Components

Once an abnormality has been found, it is important to carry out the proper repair or parts replacement without delay.
Using incompatible parts can lead to further failures, so the response must be handled carefully.

Use the following four points as a guide.

• How to decide between overhaul and replacement with genuine parts
• How to identify genuine parts quickly using a dedicated app
• How to reduce downtime by working with an authorized service center
• Guidelines for when regular maintenance and inspections should be performed

Choosing the right parts and maintaining the machine properly has a direct impact on performance.

How to Decide Between Overhaul and Replacement with Genuine Parts

If performance has declined, you need to decide whether to remove the pump for overhaul or replace it with a new one.
If the problem is limited to minor scoring or deteriorated packings, performance may be restored through cleaning and parts replacement.

However, if major components such as the pistons, cylinder block, or housing are heavily worn, partial repair will not be enough, and replacing the unit is the more reliable option.
Whenever parts are replaced, use genuine components with proven quality and durability.
Cheap third-party, counterfeit, or imitation parts often do not fit precisely and can cause recurring problems, making them unsuitable for the harsh conditions of a jobsite.

How to Identify Genuine Parts Quickly Using a Dedicated App

When you need to find the correct genuine parts on site, a dedicated app such as Kawasaki Hydraulic Finder can be extremely helpful.
In the past, identifying parts often meant searching through thick catalogs or contacting the manufacturer directly.

With a dedicated app, you can simply enter the serial number from the nameplate on a smartphone or tablet and instantly identify the correct genuine part.
This helps prevent delays caused by ordering mistakes or incompatible parts, allowing repairs to be completed more quickly.

How to Reduce Downtime by Working with an Authorized Service Center

Because hydraulic pump overhaul requires advanced skills, it is wise to rely on an authorized service center if the work is difficult to handle in-house.
Specialist technicians have manufacturer-recommended equipment and extensive experience, allowing them to detect and repair even subtle abnormalities.

If you maintain a close relationship with a service center, arranging genuine parts and securing repair support will go more smoothly when a failure does occur.
Having a cooperative relationship with skilled specialists is one of the best ways to prepare for unexpected trouble.

Guidelines for When Regular Maintenance and Inspections Should Be Performed

To keep the hydraulic system of construction equipment in good condition for as long as possible, it is important to establish and follow a regular maintenance plan in addition to daily visual inspections.
As a general guideline, filters should be replaced and a test should be performed with a dedicated measuring instrument at around every 1,000 operating hours.
It is also advisable to replace the hydraulic fluid completely at the same time.

When the machine has been used in harsh conditions involving heavy dust or muddy water, inspections should be moved forward as needed.
Rather than waiting for parts to fail, establish a preventive maintenance approach on site by replacing components in a planned way as performance begins to decline.

Summary: Extend the Service Life of Construction Equipment Through Accurate Hydraulic Pump Testing

To prevent performance loss and unexpected shutdowns in construction equipment, it is essential to use reliable genuine parts when repairs or replacement are needed.
Low-quality non-genuine parts are also available on the market, and using them can lead to poorer fuel efficiency and reduced operability.

Kawasaki Hydraulic Finder is a convenient way to confirm whether your hydraulic component is genuine and obtain accurate replacement information.
By simply entering the serial number shown on the nameplate, you can identify genuine parts, confirm accurate information, and contact an authorized dealer smoothly.
Be sure to make use of it.

Reviewed by

Ryoji Irie

Manager
After-Sales Promotion Office, Marketing & Sales Group, Precision Machinery & Robot Company, Kawasaki Heavy Industries, Ltd.

《Career History》

After joining Kawasaki Heavy Industries, I spent ten years developing the new K7V pump series as a design engineer, followed by five years at KPM (UK) as an application engineer supporting European OEMs and distributors. I am currently responsible for promoting the after-sales business globally.