Steve Bell presents an innovative new design for explosion isolation valves
Several techniques and protective devices – such as explosion venting, isolation or suppression devices – are available to contain or mitigate the major effects of an explosion in an industrial process. Major effects associated with explosions include the risk of flame and pressure wave propagation throughout the installation. The pressure waves generated by the initial explosion can cause dust in adjacent equipment or areas to become airborne again, which can trigger secondary explosions. In practice, secondary explosions are often more energetic explosions than the initial explosion in part due to compression effects in ducts and piping.
The purpose of non-return valves such as Ventex valves is to prevent pressure waves, generated by the initial explosion, from propagating throughout the installation thereby avoiding secondary explosions from happening. The Ventex valve is passive, meaning that it does not require any external source of power to operate. The energy of the initial pressure wave is sufficient to close the valve effectively blocking the pressure wave and flames and preventing any further propagation. The valve ‘isolates’ adjacent equipment and areas from the equipment where the initial explosion event took place.
Maximum explosion pressure resistance
Unlike conventional explosion non-return or flap valves, Ventex valves are able to withstand much higher explosion pressures. For example, these valves can withstand a maximum pressure of 10 bar and are a good option to protect process equipment such as hoppers designed to withstand higher pressures as well; 10 bar being generally the maximum pressure allowed in a confined environment.
The most recent series of Ventex valves, available in diameters ranging from DN100 to DN600, is now suitable for velocities up to 30m/s in the direction of the explosion, compared with 20 and 25m/s for older models. To validate the performance of the valve, numerous pre-certification tests were carried out and it was found that pressure losses are 20% lower when compared with previous models
Obviously, the seat and seal of a Ventex valve are important construction elements. The seat and seal help to ensure proper closing of the valve, leaving no space for flames to spread to other areas or equipment. In addition, they also act as a shock absorber. Seat and seal absorb the energy of the impact of the axially positioned sealing body when, under the acceleration effects of an explosion, this body hits the seat and seal.
Installation of seals on the newer models no longer require the use of special tools and seals no longer require gluing but can be mechanically inserted. This allows for an easier maintenance and reduces downtime considerably whenever seals are up for inspection and replacement.
Installation before or after bends
New generation Ventex valves guidelines allow the installation immediately before or after duct or pipe bends. Double bends or combinations of bends in different directions are also permitted. This greatly facilitates the integration of the valve into the process. The installation distances for use in an organic dust environment are extended from 2 to 15m depending on the nominal diameter of the valve.
The importance of maintenance
As an authorised service partner and dealer since the very early conception of Ventex valves, Stuvex Safety Systems has a great deal of experience with the installation and maintenance with many of these valves in a wide variety of applications and industries. Typically the company installs or maintains a Ventex valve at least once a week.
Besides providing advice regarding the installation of the valve, including turnkey installations, Stuvex Safety Systems will also assist customers with annual inspection visits, as well as the five-yearly inspection and maintenance works during which all seals require replacement. Whereas for active systems (consisting of detectors, control units and actuators), users are very aware of the need to maintain the equipment, this is not always the case for passive equipment. Periodic inspections are necessary to ensure that the inner mechanics of the valve functions properly, that there are no foreign objects hindering the valve from functioning, that there is no excessive wear or abrasion to the valve, and that the earthing connection is still in place, to name just a few.
The business of dust explosions
Stuvex Safety Systems has made explosions, and in particular dust explosions, its core business. Although at its inception it offered only electrical equipment for special Ex-applications, over the years its range and services expanded to include more equipment such as earthing and grounding systems, explosion vents, isolation valves and explosion suppression systems. It was
also one of the first on the market to offer an ATEX-certified explosion suppression system. In addition, its sister company ISMA specialises in ATEX and DSEAR risk assessments.
Steve Bell is with StuvEx Safety Systems.