Safer Valve
(continued)
It would be counter-productive to fit the RotaSafe RM if it lead to unnecessary tripping and shut down of the valve. This can be an issue if the valve is handling a product that is slightly conductive, because the product will allow a circuit to complete between the rotor and valve body. Similarly, if the valve is washed down or cleaned in place, the wash down fluid can also lead to a completed circuit and hence spurious tripping. This can be eliminated by adjusting the sensitivity of the programmable RotaSafe RM control module so that it provides an alarm only when it senses that resistance has dropped below a pre-determined level.
As the RotaSafe RM was originally designed for use in the food industry, it was imperative that it did not impede the easy to clean nature of the rotary valve. Therefore it had to be easy and fast to remove from the non drive end cover, so that the end cover itself and rotor could still be removed for quick and thorough cleaning. This means that the operator can still benefit from the unique design features of the Rota Val FCT rotary valve range, with both end covers easy to remove, fully supported on guide rails, and no rotor lifting required. This in turn leads to superior cleanliness and hygiene of the system. Of course, the RotaSafe RM can be fitted to any type of rotary valve, not only easy to clean versions.
Many will be familiar with the frustration of installing a newly serviced valve, only to find that it stalls on start up and has to be removed again. This is often due to incorrect or poor set up during re-build, meaning that the rotor clearances have not been maintained evenly, which in turn leads to the rotor fouling the valve bore. The subsequent lost production through down time, plus repair of the valve, can be very expensive. If the valve is fitted with the RotaSafe RM, there is a guard against happening, because the valve will not be allowed to start up if the rotor is not correctly fitted.
When a rotary valve is specified to handle warm product across a pressure differential, for example discharging from a dryer into a pressure conveying line, it must be specified to cater for conflicting requirements. First, the rotor to valve bore clearances need to be as small as possible in order to minimise the air leakage created by the pressure gradient. In the example, this will minimise lost conveying air and maximise the efficiency of the conveying system. However, contrary to this, the rotor clearances must be wide enough to allow for the expansion of the rotor that will occur when the warm product comes into contact with it.
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Safer Valve
(continued)
Small rotor clearances to minimise leakage can lead to contact between the rotor and the bore when the warm product enters the valve. Clearances need to be set wide enough to ensure that contact between the rotor and the valve bore cannot occur under any circumstances. This should include allowing safety margins to cater for unusual circumstances, such as low ambient and hence start-up valve body temperature, wide variations in product temperature and unusual environmental conditions. Under normal circumstances, if the rotor were to touch the bore it would be a catastrophic failure, leading to valve damage, seizure and system failure.
By fitting a rotary valve with the RotaSafe RM, such safety margins can be reduced. This is because contact between the valve bore and the rotor will lead only to an alarm from the RotaSafe RM and subsequent de-energising of the valve. It will not lead to any damage to the valve internals. The valve can then be re-started when the rotor has cooled, or even have the clearances opened up very slightly in order to prevent a re-occurrence. This means that the valve can generally operate with smaller clearances and therefore provide maximum sealing for superior system performance.
The detection circuit of the RotaSafe RM is intrinsically safe, and does not affect the ATEX compliance of any rotary valve that it is fitted to. The control module can be mounted in a safe area if required. Rota Val can supply valves that are certified for Category 1, 2 or 3 under ATEX.
When a rotary valve is specified as an ATEX “Autonomous Safety System”, it has been tested, proven and certified as able to prevent the propagation of an explosion flame-front through the valve and on into the system. This specification is often referred to as ‘flame-proof’ or ‘explosion choke’.
There are certain criteria that a valve specification must meet in order to be certified in this way, One of the most important is the clearance between the rotor vane tips and the valve bore. If this exceeds a maximum value, the flame-front will be able to pass between the vane tip and the bore and propagate a further explosion downstream of the valve. For the same reason, the bore of the valve and rotor vane tips must be in perfect condition.
If the rotor has been allowed to run in contact with the bore at any time, damage will have resulted. Even the slightest of scoring on the valve bore will have the effect of invalidating the ATEX certification of the valve, because this can open up a path through which a flame-front can propagate. If the valve is fitted with a RotaSafe RM unit, the operator can be sure that no such damage has occurred and therefore the ATEX certification will remain valid. Of course, the valve should still be monitored for wear, which can also open up rotor to bore clearances to a point where the ATEX certification becomes invalid, however this can be economically incorporated into a planned maintenance regime.
Rota Val’s Internal Sales Manager, Steve Winton, commented “Although the RotaSafe RM was originally designed for use in the food industry, it’s benefits can be applied to many other applications in many other industries as well. The unit can be fitted to a wide range of rotary valve types, including retrospectively to Rota Val and other valves. We have now supplied RotaSafe RM systems for applications in polymer handling, high temperature, food, chemicals and for use in pharmaceutical systems.”
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Safer Than the Average Valve
Safer Than the Average Valve
When leading rotary valve supplier, Rota Val, developed an innovation for the food industry, the Company also had in mind a wider brief that would benefit customers in other fields.
A high quality rotary valve will often run with very small clearances between the rotor vane tips and the valve bore itself. Clearances of 0.1mm or lower are not uncommon, depending on the characteristics and temperature of the product that the valve is handling. During normal operation, this does not present a problem and a well manufactured, correctly specified valve will run reliably with this clearance for many years.
However, under some circumstances, it can be possible for the rotor vane tips to come into contact with the valve bore. This can be down to an excessive force on the rotor due to overpressure in the system, ingress of a foreign body into the rotary valve, product build up and glazing within the valve chamber or even rotor bearing failure. Exposure to excessive temperature can also cause rotor contact due to differential expansion between the rotor and valve bore. Similarly, poor maintenance or lack of maintenance, or even incorrect re-assembly after maintenance can also lead to rotor contact with the bore.
Whilst the possibility of any of these situations arising is remote, if one does occur then the consequences can be severe and give rise to considerable expense through valve damage, lost product and production down time.
Rota Val were approached by a leading food manufacturer to address this problem. They had suffered first hand experience of rotor to bore contact causing the loss of an entire production run. This was due to contamination of the product by stainless steel that had shed from the valve rotor. It was vital, therefore to achieve a way of monitoring the rotor such that any contact with the valve bore was instantly detected, and an alarm raised to the control system.
The Rota Val RotaSafe RM Rotor Monitor achieves exactly this by constantly monitoring the electrical isolation of the valve rotor. If it should come into contact with the valve bore, thereby completing an electrical circuit, a signal is sent to the control module to instantly stop the valve. The RotaSafe RM is also self monitoring in that it will raise a second alarm if the detection circuit should be broken for any reason. Like all the best engineering this is essentially the application of a simple principle, however, by applying it carefully, many additional benefits can be offered and potential pitfalls avoided.
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rota_val_rotasafe (JPG)
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