When a system loses pressure, the cause is not always immediately obvious. In practice, many possibilities come into question: a small leak, a leaking valve, a defective process connection, a pump slowly losing pressure, a problem in the compressed air network or a fitting that does not close completely. Troubleshooting becomes particularly difficult when the pressure loss occurs only slowly or is visible only under certain operating conditions.
A digital pressure gauge is a very useful test instrument for this type of troubleshooting. It not only displays the current pressure more accurately than many simple operating pressure gauges, but depending on the version, it can also support pressure trends, min/max values or leak tests. This makes it easier to determine whether the pressure drops immediately after shut-off, slowly over several hours or only during certain switching states.
This article explains how to systematically check pressure loss in a system using a digital pressure gauge, how to build up and monitor a reference pressure and how possible causes can be narrowed down. Suitable devices can be found, among others, in the area of the DPI705E precision pressure instrument as well as in the product areas for pressure measuring instruments, calibrators and test equipment.
Table of contents
- Why pressure loss should be checked systematically
- Why a digital pressure gauge helps with troubleshooting
- Build up reference pressure and define the initial state
- Shut off the system and narrow down the test area
- Observe the pressure trend instead of reading only a momentary value
- Evaluate min/max values and pressure drop
- Document pressure drop and make it comparable
- Narrow down possible causes of pressure loss
- Pressure loss in compressed air systems
- Pressure loss in hydraulic systems
- Pressure loss at process connections, valves and fittings
- Table: Measurement pattern, possible cause and next test step
- Practical example: Compressed air system loses pressure overnight
- Which digital pressure gauge is suitable?
- Conclusion: Pressure loss becomes visible when the pressure trend is measured properly
- FAQ: Frequently asked questions about pressure loss testing with a digital pressure gauge
Why pressure loss should be checked systematically
Pressure loss is initially only a symptom. It does not yet indicate where the fault is located. When the pressure in a system drops, the cause may be in the tested section itself, but also in adjacent components. A pump may lose pressure backwards, a check valve may leak, a shut-off valve may not close completely, a fitting may have a minimal leak or a consumer may reduce pressure unnoticed.
Without systematic testing, troubleshooting is often carried out in the wrong place. A pipe is checked even though the problem is in the valve. A pump is suspected even though there is a small leak in the network. Or a pressure gauge is suspected as the cause, although it is only displaying the actual pressure loss.
Troubleshooting should therefore always consider the pressure trend. The decisive factor is not only that the pressure drops, but when, how quickly and under which conditions. Does the pressure drop immediately after shut-off? Does it initially remain stable and only fall after a longer period? Does the pressure loss occur only when the system is running? Or only during standstill?
This is exactly where the advantage of a digital pressure gauge lies. It makes small pressure changes more visible and helps assess the time-based trend. This allows the cause to be narrowed down step by step.
Why a digital pressure gauge helps with troubleshooting
A digital pressure gauge offers several advantages over a simple mechanical pressure gauge. It is often easier to read, has a higher resolution and can display small pressure changes more clearly. This is particularly important when searching for slow pressure loss, because the pressure drop is often not immediately obvious.
Many digital pressure gauges offer additional functions that are helpful during troubleshooting. These include min/max memory, hold function, tare function, leak test, filter function or accurate display with different pressure units. Depending on the device, documentation or data recording may also be possible.
A mechanical operating pressure gauge often only roughly indicates whether pressure is present. This is often not sufficient for troubleshooting. If the pressure drops overnight from 7.2 bar to 6.4 bar, the change is harder to assess on a coarse analogue gauge than on a digital pressure gauge with suitable resolution.
However, it is important that the digital pressure gauge matches the measuring range. A device with too large a measuring range may resolve small pressure losses less precisely. A device with too low a measuring range can be overloaded. The measuring range should therefore be selected to match the system and the expected test pressure.
Build up reference pressure and define the initial state
The test begins with a defined initial state. The system or the section to be tested is brought to a suitable reference pressure. This pressure should match the application and remain within the permissible limits of all components involved. Pressure must not simply be increased arbitrarily just to make pressure loss visible more quickly.
The reference pressure should be reached in a stable manner. After filling or pressurizing, the pressure may initially still change slightly because temperature, medium, lines and volume equalize. Especially with gases and compressed air, temperature changes can influence pressure. It is therefore useful to allow a short stabilization time before the actual assessment.
The digital pressure gauge is connected at a suitable measuring point. This measuring point should be as representative as possible for the area being tested. If measurement is carried out at an unsuitable location, the pressure trend can be distorted by local effects, valves or restrictions.
The initial value is documented. This includes pressure, time, operating state, temperature conditions, measuring point and, where applicable, the position of relevant valves. Only then can the later pressure drop be assessed meaningfully.
Shut off the system and narrow down the test area
To find the cause of pressure loss, the test area must be narrowed down. For this purpose, a section of the system is shut off. The aim is to determine whether the pressure loss occurs inside this section or whether it is caused by adjacent areas.
In a compressed air system, for example, the entire network can be checked first. Individual pipe sections, machine connections or consumer groups are then shut off one after another. If the pressure loss is significantly stronger in one section, the search can be focused on that area.
In hydraulic systems, valves, cylinders, accumulators, lines or pump sections can be considered separately. If the pressure remains stable after a certain valve has been shut off, the cause is probably outside the isolated area. If the pressure continues to fall, the cause is located inside the tested section or at the shut-off device itself.
It is important that shut-off valves themselves are tight. A leaking shut-off valve can falsify the test. It then appears as if the tested section is losing pressure, although the pressure is escaping through the valve into another area.
Observe the pressure trend instead of reading only a momentary value
A single pressure value says very little. The trend over time is decisive. Therefore, the pressure after shut-off should not be read only once. It is better to observe the pressure over a defined period and record several measurement points.
A rapid pressure drop immediately after shut-off often indicates a larger leak, an open valve, an incorrectly isolated test area or a problem at the measuring connection. A slow pressure drop over several hours is more likely to indicate small leaks, minor internal leakage or temperature-related influences.
A pressure that is initially stable and drops later can also be informative. A valve may only open under certain conditions, a consumer may switch on, a temperature change may influence the medium or a check valve may only seal intermittently.
A digital pressure gauge with min/max function or leak test can help identify such trends more easily. For longer tests, data recording is particularly useful because the pressure trend then does not have to be monitored manually.
Evaluate min/max values and pressure drop
Min/max values are very useful during troubleshooting. The maximum value shows the highest pressure reached, while the minimum value shows the lowest pressure during observation. This allows the pressure drop over the test period to be determined.
Example: A system is pressurized to 8.0 bar. After 60 minutes, the digital pressure gauge shows a minimum value of 7.6 bar. The pressure drop is therefore 0.4 bar within one hour. This value is significantly more meaningful than the general statement “the system is losing pressure”.
It is important to always relate the pressure drop to time. A loss of 0.2 bar in five minutes must be evaluated differently from 0.2 bar over twelve hours. Volume, medium, temperature and the permissible leakage rate of the system also play a role.
For repeated measurements, the conditions should be as similar as possible. If one measurement is taken while the system is warm and another while it is cold, the results can differ. Especially with gases, temperature changes can significantly affect pressure.
Document pressure drop and make it comparable
Good documentation is essential when pressure losses are to be compared, assessed or later traced. It is not enough to note only the final pressure. Start pressure, final pressure, test duration, medium, measuring point, temperature conditions, system state and the position of relevant valves are important.
If the test is part of maintenance or troubleshooting, observations should also be documented. These include noises, visible leaks, condensate, oil traces, switching states, pump run times or consumer behaviour. This information helps to technically classify the pressure loss later.
For recurring problems, trend measurement is particularly helpful. If pressure loss is compared over several nights or operating states, patterns can be identified. A pressure drop only at the weekend may indicate different causes than a pressure drop during ongoing operation.
Clean documentation turns a simple pressure measurement into a reliable diagnosis. It also helps when communicating with service, maintenance, manufacturers or customers.
Narrow down possible causes of pressure loss
Pressure loss can have many causes. In compressed air systems, leaks at hoses, couplings, fittings, valves or consumer connections are common. In hydraulic systems, internal leakage can occur at valves, cylinders or pumps. In process plants, seals, fittings, pressure connections and measuring points are typical areas to check.
The type of pressure drop provides initial indications. A very rapid pressure loss is more likely to indicate a larger leak or an open path. A slow pressure loss is more likely to indicate small leaks, internal leakage or temperature-related pressure changes. Pressure loss only under load can indicate consumers, switching valves or dynamic seals.
It is useful to divide the system step by step. First a large area is tested, then smaller sections. This allows the fault to be narrowed down spatially. At the same time, typical weak points should be checked: fittings, quick couplings, hoses, valve seats, check valves, process connections, pressure regulators and vents.
A digital pressure gauge does not directly show the leaking point. However, it shows when and how pressure is lost. This information is the basis for targeted troubleshooting.
Pressure loss in compressed air systems
Compressed air systems often lose pressure due to small leaks. These can occur at couplings, hoses, valves, maintenance units, cylinders, machine connections or pipes. A single small leak is often difficult to hear. Many small leaks together, however, can cause considerable energy losses.
For testing, the compressed air network is brought to a defined pressure and then shut off. If the pressure drops significantly overnight, this indicates leaks or leaking consumers. Individual areas can then be tested separately.
A rapid pressure drop immediately after shut-off indicates a larger leak or a consumer that is still open. A slow pressure drop over many hours can indicate smaller leaks. In both cases, the digital pressure gauge helps make the loss measurable.
With compressed air, it should also be considered that temperature changes influence pressure. If the system cools down after operation, pressure can drop even without a leak. Temperature and operating state should therefore be considered during evaluation.
Pressure loss in hydraulic systems
In hydraulic systems, pressure loss can be caused by external leaks or internal leakage. External leaks are often visible, for example through oil traces at fittings, hoses or seals. Internal leakage is more difficult to detect because the medium can flow past valves, cylinders or pumps inside the system.
A digital pressure gauge can help observe the pressure drop in an isolated hydraulic section. If the pressure drops despite closed valves, internal leakage may be present. In cylinders, slow drifting under load can indicate internal leakage.
Hydraulic tests must be carried out with particular care because high pressures can occur. Measuring range, pressure connection, hoses and adapters must be suitable for the test pressure. Pressure spikes during switching or relief must also be considered.
Pressure loss testing does not replace a complete hydraulic diagnosis, but it provides important information about whether a pressure circuit remains stable or loses pressure internally.
Pressure loss at process connections, valves and fittings
In process plants, pressure losses can occur at many points. Typical causes include leaking valve seats, seals, flanges, threaded connections, diaphragm seals, impulse lines, vents or drain points. Very small leaks are not always immediately visible, but can still influence the pressure trend.
During testing, the measuring point should be as close as possible to the area to be assessed. Long measuring lines or unsuitable connection points can distort the result. If a digital pressure gauge is connected via adapters or hoses, these connections must also be tight. Otherwise, a leak in the test setup may be incorrectly interpreted as a system fault.
Valves deserve special attention. A valve may appear tight from the outside but may not close completely internally. The pressure in the shut-off section then drops even though no visible leak is present. Such behaviour can be narrowed down by targeted shut-off and comparison of different sections.
For process media, material compatibility, temperature, pressure range and safety requirements must also be considered. The digital pressure gauge and all connection components must be suitable for the medium and application.
Table: Measurement pattern, possible cause and next test step
| Measurement pattern | Possible cause | Next test step |
|---|---|---|
| Pressure drops sharply immediately after shut-off | Larger leak, open valve, incorrect test area or leaking measuring connection | Check shut-off position, measuring connection and visible leak points |
| Pressure drops slowly over several hours | Small leak, internal leakage, temperature drop or leaking shut-off valve | Repeat test, consider temperature and isolate sections individually |
| Pressure initially remains stable and drops later | Switching state changes, valve opens, temperature changes or consumer becomes active | Compare pressure trend with operating states |
| Pressure drops only while the system is running | Consumer, pump, control valve or dynamic seal involved | Carry out measurement under different operating states |
| Pressure drops only during standstill | Check valve, internal leakage or consumer relieves the pressure circuit | Check return paths and shut-off valves |
| Pressure fluctuates strongly | Pump, regulator, compressed air consumer or process fluctuation | Record min/max values and check measuring point |
| Pressure drop only with cold system | Temperature-related pressure change or seal behaves temperature-dependently | Document temperature and repeat measurement under comparable conditions |
| Pressure drop disappears after changing the test setup | Adapter, hose or connection of the test instrument was leaking | Check the test setup separately for tightness |
Practical example: Compressed air system loses pressure overnight
A workshop notices that the pressure in the compressed air network drops significantly overnight. In the morning, the compressor has to run longer until operating pressure is reached again. Initially, it is unclear whether the network is leaking, whether a consumer is losing pressure or whether the pressure drop is caused by temperature changes.
For the test, a digital pressure gauge is connected at a suitable measuring point in the compressed air network. The system is brought to normal operating pressure in the evening. The compressor is then disconnected from the network and the section to be tested is shut off. The start pressure is documented.
Immediately after shut-off, the pressure initially remains stable. After several hours, however, it slowly drops. This speaks less for a large open leak and more for smaller leaks or leaking consumers. In the next step, individual pipe sections and machine connections are tested separately.
At one specific machine branch, the pressure drop is significantly greater than in the rest of the network. Several quick couplings, a hose and a valve are checked there. One coupling is slightly leaking, and a consumer slowly vents through an internal valve. After repair, the measurement is repeated. The pressure now remains significantly more stable overnight.
The example shows how important the time-based trend is. If only the final pressure in the morning had been considered, the cause would have been difficult to narrow down. Measurement with the digital pressure gauge made it visible when the pressure dropped and which area was particularly affected.
Which digital pressure gauge is suitable?
For troubleshooting pressure loss, the digital pressure gauge should match the pressure range, medium and test setup. Important factors are a suitable measuring range, sufficient accuracy, good resolution, robust connections and an appropriate pressure unit. For mobile service tasks, ease of operation, housing protection and battery life are also important.
Useful functions include min/max memory, tare, hold, filter function or leak test. For longer tests, recording the pressure trend can be useful. This allows the pressure drop over time to be documented without constant manual reading.
A device such as the DPI705E precision pressure instrument is suitable for many service and test tasks where accurate pressure measurement, robust handling and practical functions are required. Depending on the application, measuring range and pressure connection must be selected appropriately.
For very small pressure ranges, high pressures, aggressive media, hydraulic tests or tests requiring documentation, special versions or additional adapters, hoses and calibration accessories may be required. The entire measuring chain is always decisive: measuring instrument, connection, adapter, hose, medium and test procedure.
Conclusion: Pressure loss becomes visible when the pressure trend is measured properly
Pressure loss in a system can only be reliably narrowed down if the pressure trend is checked systematically. A single pressure value is rarely sufficient. The decisive factors are how quickly the pressure drops, when the pressure drop begins and under which operating conditions it occurs.
A digital pressure gauge helps make small pressure changes visible, evaluate min/max values and document pressure drop over time. By selectively shutting off individual system areas, it can be narrowed down step by step whether the cause lies in a leak, a valve, a pump, a consumer, a process connection or in the test setup itself.
Anyone who wants to test pressure loss professionally should clearly document reference pressure, measuring point, test duration, temperature conditions and system state. This turns a simple pressure measurement into reliable troubleshooting that significantly supports maintenance, service and system operation.
FAQ: Frequently asked questions about pressure loss testing with a digital pressure gauge
How do you find pressure loss in a system?
The area to be tested is brought to a defined reference pressure, shut off and observed over a specified period using a digital pressure gauge. The pressure drop is then evaluated and the system area is narrowed down step by step.
Why is a digital pressure gauge better than a normal pressure gauge?
A digital pressure gauge usually offers better resolution, more accurate reading and additional functions such as min/max memory, hold or leak test. This makes small pressure changes easier to detect.
What does it mean if the pressure drops immediately after shut-off?
An immediate pressure drop can indicate a larger leak, an open valve, an incorrect test area or a leaking measuring connection.
What does a slow pressure drop over several hours mean?
A slow pressure drop often indicates small leaks, internal leakage, a leaking shut-off valve or temperature-related pressure changes.
Can temperature falsify pressure loss?
Yes. Temperature affects pressure, especially with gases and compressed air. If the system cools down, the pressure can drop without necessarily indicating a leak.
How do you test a compressed air system for pressure loss?
The compressed air network is brought to operating pressure, shut off and the pressure trend is observed over time. Individual pipe sections or consumers are then tested separately.
How long should a pressure loss test take?
This depends on the system, volume, medium and expected leak. For quick faults, a few minutes are often enough. For small leaks or compressed air networks, several hours or an overnight test are useful.
Which functions should a digital pressure gauge have for troubleshooting?
Helpful functions include good resolution, suitable measuring range, min/max memory, hold function, tare, filter function, leak test and, depending on the application, data recording.
Can a leaking measuring connection falsify the test?
Yes. If adapters, hoses or the connection of the digital pressure gauge are leaking, it looks as if the system is losing pressure. The test setup itself must therefore be tight.
How do you narrow down the cause of pressure loss?
The system is divided into smaller sections and tested one after another while shut off. The area with the strongest pressure drop is then examined more closely.
What causes pressure loss?
Possible causes include leaks, leaking valves, defective check valves, internal leakage at cylinders or pumps, leaking process connections, consumers, pressure regulators or faulty measuring connections.
Which digital pressure gauge is suitable for pressure loss tests?
The device must match the pressure range and medium. For many service and test tasks, a robust digital pressure gauge such as the DPI705E precision pressure instrument is a suitable solution.