By-pass made with our Rotary Selector Valve (RSV)

In some processing plants, liquid chemicals are stored in large vessels where the fluid flow into and out of each vessel is controlled by in-line valves. Pneumatic control of the actuators that open or close these in-line valves is generally accomplished by sending an electrical signal from the control centre to remote solenoid valves that in turn pressurise or vent the actuators. This forms part of the process at nuclear power stations that require high quality feed water used for cooling. Domestic towns water is processed to produce demineralised (pure) water for boiler feed purposes.

RSV series 60

On occasions, for example to overcome failure or carry out planned maintenance, it is necessary to by-pass the automatic process and therefore the aforementioned solenoid(s). Installation of a Drallim rotary selector valve (RSV) enables manual override of this automatic control by providing an alternative air path.

Single acting actuators (for instance those which spring return when the electrical signal is removed and hence no pressure is supplied to move the actuator) are controlled by a single pneumatic signal. These can therefore be bypassed using a single bank RSV having one air path through. Double acting valves that require one side to be pressurised whilst the other vented side is piped away employ a 2 bank valve. Multiple actuators can be controlled by a single RSV having up to six separate banks.

Each RSV bank is pneumatically independent but linked by a common central spindle, enabling separate air paths to be controlled concurrently; each output is effectively a valve in itself. The RSV can incorporate an integral electrical rotary switch which allows fluid and electrical circuits to be controlled simultaneously, or can be used simply to provide positional indication remotely at the control centre.

Drallim RSVs and tube couplings were specified and installed in the Make Up Water Treatment and Condensate Polishing Plants at a number of nuclear power stations throughout the U.K. when they were originally brought into service.
Many of these valves therefore date back to the 1970’s and 1980’s and are still in service. As part of on-going improvement projects some are however being replaced, along with associated pneumatic equipment which includes the aforementioned solenoid valves.
The ageing of perishable internal seals is a contributing factor in making this decision, as the valves themselves are still serviceable. Initially Drallim were tasked to carry out site surveys and produce recommendation reports, together with CAD generated circuits.
The reports listed possible areas for improvement and demonstrated a thorough understanding of the operational requirements.
Drallim are not only supplying the RSVs, but the complete replacement pneumatic control consoles, which they design and build in-house. On-site installation and commissioning is also carried out by Drallim staff.

The RSV is a rotary selector or distributor for use in small bore piping systems at pressures up to 10bar. It is a relatively simple and therefore extremely reliable unit, based on a modular design and as such configurable for a multitude of applications.
It is custom built from stock parts. The PIV body is manufactured in brass or stainless steel, both having stainless spindles, and can have stems and seals in differing materials to suit the media being used.

control console

The valve was first introduced in the late 1950’s, has remained largely unaltered, and due to its versatility is widely used in industry for a vast range of applications involving the switching of liquids, vapours and gases.

The same technique as described in this application is employed in automated manufacturing plants where manual override in safety critical situations is required. The RSV is used extensively in hostile environments such as offshore platforms.


David Elliott, Drallim Technical Manager, 07 October 2013. 03/10/2008

Permanent Current Rail Indicator Device – P-CRID

Tube Lines (TFL London Underground).

TFL London Underground

Every night workers maintain and upgrade the London Underground and their protection is paramount. Work cannot start before passenger trains are taken out of service and the track current is turned off. Only then can certificated Protection Masters trained to use a handheld device access the track to test that the 630V DC traction current is actually off.
Tube Lines developed a prototype permanent trackside device (P-CRID) to protect engineers from live currents when they are working on the Underground.

The P-CRID means the Protection Master no longer steps on to the track to check traction current. Track teams can view the device from a place of safety until it shows that the current is off. As renewal and maintenance works continue through the early hours the device shows a continuous indicator on current status. The P-CRID has back-lit visual panels and emits audio beeps to show status.

P-CRID unit (v1)

With a prototype built and successful field trials completed Tube Lines required a contract manufacturer to optimize the design and manufacture 600 units. With a short lead time and installation schedule they went to tender.
Drallim Industries were the successful company. With only a prototype and minimal drawings their engineering team went into action. An engineer from Tube Lines was based in-house at Drallim’s manufacturing facility in East Sussex to approve the design and sign off drawings as they were produced so components could be purchased as soon as possible.

Software changes and PCB layout modifications were carried out by Drallim engineers to meet the latest operation and EMC requirements. The final certification required before manufacturing could commence was to ensure the enclosure met the required environmental rating. Again Drallim’s engineers performed the IP testing in-house and with all the documents signed and approved by Tubelines the manufacturing process could commence.

Drallim created a dedicated production line for the assembly of the P-CRID’s. Purpose built manufacturing jigs; tooling and test equipment were also designed and built with an interlocked test area created for the high voltage testing of the completed assemblies.
With just a four-hour work window between last and first trains on the London Underground, the innovation has seen a much improved balance of efficiency and safety. The P-CRID has been described as one of the biggest safety improvements made in the industry for decades

The P-CRID is constantly self-checking itself and is always fail safe, giving the track teams confidence about the state of track current.
So far 600 P-CRIDS have been installed across the Jubilee, Northern and Piccadilly lines and have a design life of 25 years. The team behind this groundbreaking device designed, built, assured, and commenced installation within just 12 months – a timeframe unheard of in the rail industry for such a major improvement. The company is sharing the innovation with other railways and the rest of the Underground.