FEMA Pressure Switches

FEMA pressure switch keeps switching on and off: causes and solutions

If a pressure switch keeps switching on and off, it may initially seem as if the device is defective. In many cases, however, the cause is not the pressure switch itself, but the setting, an incorrect switching range, pressure pulsations or an unsuitable installation location.

Especially in pumps, compressors, hydraulic systems or filter monitoring applications, a pressure switch that switches too frequently can lead to contact wear, false alarms, unnecessary downtime or unstable system behavior. The cause should therefore be checked systematically.

This article explains typical reasons for frequent switching, contact bounce or contact chatter and shows how such problems can be avoided in practice.

You can find an overview of suitable devices in our category
FEMA pressure switches.

Why does a pressure switch switch too frequently?

A mechanical pressure switch switches as soon as the set pressure value is reached. If the pressure then falls or rises beyond the reset point again, the contact changes its state again. This behavior is basically normal.

It becomes problematic when the pressure switch switches very quickly in succession or when the contact chatters due to small pressure fluctuations. In practice, this is often referred to as contact bounce, contact chatter or frequent cycling.

• With stable pressure conditions the pressure switch should only switch when an actual limit value is exceeded.
• With fluctuating pressure the switching point may be reached several times in succession.
• With an insufficient switching differential the reset point is too close to the switching point.
• With strong pressure pulsations the switching element is subjected to high mechanical stress.
• With incorrect device selection the pressure range does not match the application.

For many industrial applications with liquids and gases, the
FEMA pressure switches for liquids and gases
are suitable.

Typical symptoms during system operation

A pressure switch that switches frequently can become noticeable in different ways depending on the system. Some symptoms are immediately visible, while others only appear through faults, error messages or increased wear.

Symptom	Possible cause	Typical consequence
Contact switches rapidly back and forth	Switching point is within the range of normal pressure fluctuations	Unstable control, contact wear
Pump starts and stops frequently	Hysteresis too small or pressure accumulator too small	High switching frequency, mechanical stress
Switch reacts to every pressure peak	Pulsations or pressure surges in the line	False alarms or unnecessary shutdowns
Switching point appears inaccurate	Unsuitable installation location or contaminated pressure line	Fluctuating switching behavior
Device switches too early or too late	Incorrect pressure range or incorrect setting	Unreliable system function

Cause 1: The switching point is too close to the operating pressure

One of the most common causes is an incorrectly selected or unfavorably set switching point. If the switching point is directly at the normal operating pressure, even small pressure fluctuations can be enough to actuate the contact repeatedly.

Example: A system normally operates between 4.8 and 5.2 bar. If the pressure switch is set to 5.0 bar, the switching point lies in the middle of the normal operating range. The pressure switch may then switch on and off continuously, even though the system is technically operating correctly.

Typical signs

• The pressure switch switches particularly frequently during normal operation.
• The fault does not occur continuously, but only during certain operating states.
• The system pressure gauge shows fluctuating values around the switching point.
• After a slight adjustment of the switching point, the behavior becomes more stable.

Practical solution

The switching point should be set with sufficient distance from the normal operating pressure. In addition, the reset point must also be taken into account. Only when both values match the system will the pressure switch operate reliably.

Situation	Assessment	Recommendation
Operating pressure fluctuates around the switching point	Unfavorable setting	Select a switching point with greater distance
Switching point is at the edge of the setting range	Device range may be unsuitable	Check pressure switch with a more suitable range
Pressure fluctuates strongly during normal operation	System generates dynamic pressure changes	Check switching differential, damping and installation location

Cause 2: The switching differential or hysteresis is too small

The switching differential, also known as hysteresis, is the distance between the switching point and the reset point. If this distance is too small, the pressure switch can reset immediately after only slight pressure changes.

Especially in pump controls, compressors and systems with fluctuating pressure, a sufficiently large switching differential is important. It ensures that the system does not switch again with every small pressure movement.

Term	Meaning	Example
Switching point	Pressure value at which the contact is actuated	Switching at 6 bar
Reset point	Pressure value at which the contact switches back	Reset at 5.5 bar
Switching differential	Distance between switching point and reset point	0.5 bar

Typical mistakes

• Only the switching point is considered, not the reset point.
• The natural pressure fluctuation of the system is greater than the switching differential.
• A device with insufficient or unsuitable hysteresis is used.
• The pressure switch is used for pump control even though the switching differential does not match the system.

For standard applications in mechanical engineering, hydraulics and pneumatics, universal pressure switches such as the
DCM3 universal pressure switch
or devices from the
DCM/DNM pressure switch and pressure monitor series
are often used.

Cause 3: Pressure pulsations caused by pumps or compressors

Pumps, compressors and fast-switching valves can generate pressure pulsations. These short pressure fluctuations are transmitted directly to the pressure switch via the pressure line. As a result, the pressure switch may trip even though the average process pressure is actually uncritical.

Applications with piston pumps, diaphragm pumps, compressors, hydraulic power units or long, rigid pressure lines without damping are particularly critical.

Typical signs of pressure pulsations

• The pointer of a pressure gauge vibrates or jumps.
• The pressure switch switches particularly when a pump starts or stops.
• The problem only occurs at certain speeds or flow conditions.
• A short pressure surge triggers an alarm or shutdown.
• The contact switches more frequently than the actual process condition would suggest.

Cause	Effect on the pressure switch	Possible measure
Piston pump	Periodic pressure peaks	Damping, suitable installation location, larger switching differential
Compressor	Fast pressure changes during cycling	Check switching point and reset point
Fast-closing valve	Pressure surge in the line	Reduce pressure surge, decouple line
Long rigid pressure line	Transmission of vibrations	Check stabilized measuring point or restrictor

Cause 4: Incorrect installation location or unsuitable pressure line

Not only the pressure switch itself, but also the installation location influences the switching behavior. If the pressure is tapped directly downstream of a pump, at a valve, at a restriction or on a strongly vibrating line, the measured pressure can fluctuate significantly.

An unsuitable installation location can cause the pressure switch to monitor local pressure peaks, flow effects or vibrations instead of the stable process pressure.

Unsuitable installation locations

• directly at the pump outlet
• directly downstream of fast-switching valves
• at pipe bends with strong flow changes
• on strongly vibrating lines
• at contaminated or partially blocked pressure connections
• at measuring points with air bubbles, condensate or deposits

Better approach

The pressure should be tapped at a representative and stable point wherever possible. With pulsating media, suitable damping or modified line routing can be useful. It should also be checked whether the pressure connection is clean and free of deposits.

Cause 5: Incorrect pressure range selected

A pressure switch should not merely roughly match the desired switching point. The entire setting range must suit the application. If a pressure range that is too large or too small is selected, the switching behavior may become inaccurate, overly sensitive or unsuitable.

A very large pressure range can be unfavorable for small switching points because fine adjustment becomes more difficult. A range that is too small, on the other hand, can cause the switching point to be at the edge of the range or pressure peaks to overload the device.

Selection error	Possible consequence	Better solution
Pressure range too large	Switching point is harder to set precisely	Select a more suitable setting range
Pressure range too small	Pressure peaks can stress the device	Consider maximum pressure and pressure peaks
Switching point is at the end of the range	Unfavorable switching behavior possible	Check device with a more suitable range
Medium not considered	Material or temperature problems possible	Check medium, temperature and seal

You can find a structured overview of different series in the category
FEMA pressure switches.

Practical solutions against frequent switching

If a pressure switch switches too frequently, the device should not be replaced immediately. Often, the problem can be narrowed down through proper technical checks.

Possible measures

• Check switching point: Is the switching point too close to the normal operating pressure?
• Calculate reset point: Does the switching differential match the pressure fluctuation of the system?
• Observe pressure curve: Are there pressure peaks, pulsations or fast pressure changes?
• Check installation location: Is the pressure measured at a stable and representative point?
• Check pressure connection: Are there contaminations, deposits or blockages?
• Check medium: Are materials, seals and temperature limits suitable?
• Check device range: Is the pressure range suitable or is it too large or too small?
• Check approvals: Are there special requirements due to hazardous area, steam, gas or safety function?

Problem	Check	Possible solution
Pressure switch reacts to small fluctuations	Check switching point and reset point	Change switching point or select device with suitable switching differential
Switch reacts to pressure peaks	Observe pressure curve with pressure gauge or measuring device	Check damping, stable measuring point or line adjustment
Pump cycles frequently	Check operating pressure, accumulator size and hysteresis	Adjust switching differential and system parameters
Switching point is difficult to set	Compare setting range with desired switching point	Select a more suitable pressure range
Switch behaves noticeably only at times	Check operating states, temperature and medium	Narrow down cause depending on process condition

When is another FEMA pressure switch useful?

Another pressure switch is useful if the application does not match the existing device. This can concern the pressure range, switching differential, medium, temperature, approval or device function.

A replacement should be checked if:

• the desired switching point is at the edge of the setting range,
• the switching differential does not match the process,
• pressure peaks reach or exceed the maximum permissible pressure,
• the medium requires different materials or seals,
• the application is safety-related,
• Ex approval is required,
• differential pressure actually needs to be monitored instead of relative pressure.

For safety-related applications with hot water, steam, gas or liquid fuels, special pressure monitors such as the
DWR pressure monitor
may be suitable.

If not the absolute pressure but the pressure difference between two measuring points is decisive,
FEMA DDCM differential pressure monitors
may be the more suitable solution.

Troubleshooting checklist

This checklist helps systematically narrow down many causes of frequent switching.

Check question	Why is it important?	Assessment
Is the switching point within the normal operating range?	Then normal pressure fluctuations may already cause switching.	Select switching point with distance from operating pressure.
Is the switching differential sufficiently large?	Insufficient hysteresis causes frequent resetting.	Calculate reset point and compare with pressure curve.
Are there pressure pulsations?	Pumps and compressors generate fast pressure changes.	Check damping or stable measuring point.
Is the installation location suitable?	Local pressure peaks can distort the switching behavior.	Select measuring point at representative position.
Does the pressure range match?	An incorrect range makes stable adjustment more difficult.	Check device with more suitable setting range.
Is the pressure connection clean?	Contamination can delay or distort pressure transmission.	Check connection and line.
Does the medium match the device?	Temperature, material and seal affect function.	Compare technical data with application.
Are special approvals required?	Hazardous areas, steam, gas or safety functions require suitable versions.	Check approval and device function.

Conclusion: frequent switching is usually a selection or application problem

If a FEMA pressure switch keeps switching on and off, this does not automatically mean that it is defective. Often the actual cause is the switching point, switching differential, pressure pulsations, installation location or an unsuitable pressure range.

It is important to check the application systematically. The normal operating pressure, pressure fluctuations, reset point, medium and possible pressure peaks should be considered together. Only then can it be reliably assessed whether a different setting, a changed installation location or another pressure switch is required.

You can find a suitable preselection in our category
FEMA pressure switches.

FAQ: frequently asked questions about pressure switches that switch too frequently

Why does my pressure switch keep switching on and off?

The switching point is often too close to the normal operating pressure, or the switching differential is too small for the pressure fluctuations in the system. Pressure pulsations, an unsuitable installation location or an incorrect pressure range can also be the cause.

What does contact bounce mean in a pressure switch?

In connection with pressure switches, contact bounce is often used when the contact switches rapidly in succession or chatters. This can be caused by small pressure fluctuations directly at the switching point, vibrations or electrical contact loads.

What does hysteresis have to do with frequent switching?

Hysteresis, or switching differential, ensures that the pressure switch does not immediately switch back. If this difference is too small, even a slight pressure change can trigger another switching operation.

Why does the pump keep switching on and off?

In pump systems, frequent cycling can be caused by an insufficient switching differential, a pressure accumulator that is too small, pressure losses, leaks or an unfavorable switching point setting. The pressure curve should be checked during operation.

What can be done against pressure pulsations?

Depending on the system, a stable measuring point, suitable damping, a modified pressure line or a pressure switch with a suitable switching differential can help. It is important that the pressure switch does not process every short pressure peak directly as a limit value exceedance.

Can an incorrect pressure range cause frequent switching?

Yes. If the pressure range does not match the application, the switching point may be unfavorable or difficult to set reliably. The desired switching point should not be directly at the edge of the setting range.

Which FEMA pressure switch is suitable for general industrial applications?

For many standard applications in mechanical engineering, pneumatics or hydraulics, universal pressure switches are suitable. One example is the
DCM3 universal pressure switch. However, pressure range, medium, switching differential, connection and contact function are always decisive.

When is a differential pressure switch the better solution?

A differential pressure switch is useful when it is not the absolute pressure but the pressure difference between two measuring points that needs to be monitored. This is the case, for example, in filter monitoring, pump protection or flow monitoring.
FEMA DDCM differential pressure monitors
can be used here.

What should be considered in safety-related applications?

In safety-related applications, a standard pressure switch is often not sufficient. Depending on the system, special pressure monitors, pressure limiters, approvals or manual reset functions may be required. For hot water, steam, gas and liquid fuels, for example, the
DWR pressure monitor
may be relevant.

Where can I find an overview of FEMA pressure switches?

You can find a structured overview in the category
FEMA pressure switches. It includes various series for liquids, gases, differential pressure, hazardous areas and safety-related applications.