Are Monitored Valves Really Safe?



Formerly both hydraulic and pneumatic valves did not have multiple circuits for external monitoring devices and certainly didn’t have any form of positive guidance for protection when in a single spool or poppet configuration. They were like a gate or guard circuit requiring full monitoring as there was no further redundancy to protect the system from failure. Since those days, there has been three primary forms of valve monitoring techniques used…find out more in the article below.

Development and History of Monitored Valves

During recent years there have been many developments within the safety industry for hydraulics and in particular pneumatic valves. These systems have predominately been applied to press applications and primary fluid power machine supply.




Historically, industry was on a trend to treat fluid power directional control valve monitoring whether it be hydraulic or pneumatic with the same regard as to a three-phase electrical contractor. This meant monitoring an auxiliary contact of the device and incorporating this contact within the feedback control loop of a certified safety relay.



What was overlooked in these applications is a three-phase contactor applied in a safety application is generally of a positive guided device where three separate contacts along with an auxiliary contact are being switched. Should one contact stick or become welded, the other contacts will break.




There is also additional redundancy within this form of monitoring by the added security of either a thermal overload or motor circuit breaker, whereas should a contactor fail, the contactor may permit one phase to remain connected, in which case the motor protection would provide the additional redundancy therefore shutting down the control system with a feedback monitoring contact to indicate a system failure.

Forms of Valve Monitoring

Forms of Valve Monitoring

The Story of Fluidsentry


In 2001, our founder Murray Hodges, noticed challenges system designers were facing. Mainly in meeting safety requirement regarding the integrity of fluid power safety control system.


And while there were several products available in Europe and Australia for safety applications; manufacturers could not demonstrate compliance with the key standards that outline the requirements for the safety related parts of control systems.



Although there were many electronic safety devices in the market, nothing could safety interlock with pneumatic or hydraulic devices. Therefore, Murray developed a global solution. The first monitored pneumatic safety valve, using positive driven high precision safety switching for the monitoring function. We are still using the technology 20 years later!


Today, Fluidsentry has joined Fortress Safety and have continued to expand the range of its monitored hydraulic and pneumatic valves. By doing so, assisting the industry in complying with AS4024.1 and ISO 13849 requirements.

Products Mentioned in this Article

Hydraulic Monitored Safety Valves

Fluid Power Safety

Pneumatic Monitored Safety Valves

Fluid Power Safety