Use of Residual Pressure Valves - Challenges and Opportunities for Indian subcontinent. Presented By: Rohit Behani

Do you expect a different (read better) result but shy away from new solutions?

Why the need for Residual Pressure valves (RPV)? Despite warning notices on gas cylinders and customer information, gas users do not always follow good operating practice like leaving a small positive pressure in the gas cylinder or closing the cylinder valve after use. The concept of a cylinder valve that retains a small positive pressure (1-5 Bar) in a gas cylinder even if the valve is inadvertently left open has been in use for many years around the world. The benefits include preventing the possibility of back contamination, maintaining a high gas quality, reducing internal cylinder maintenance and improving cylinder life. Use of RPV eliminates high cost of purging, vacuum and cleaning of gas cylinders. Reports from the EIGA Cylinder Data Base indicate that approximately 30% of all cylinder incidents reported were the result of internal corrosion which could have been avoided by use of RPV. (Source :EIGA IGC Doc 64/05/E) Benefits

How it works? Working Principle 1.The Residual Pressure Unit consists of brass housing, O-ring to seal the housing into the valve body, spring, piston with quad ring and a small O-ring to seat the Residual Pressure unit against spring force. 2.When the valve is in the closed position, the piston is under spring force against the valve body sealing surface and the small O-ring seals the outlet off against the atmosphere. 3.When the main valve is opened, contents of the cylinder flows through the valve to the front side of the piston. 4.When the force exceeds the spring load, the piston is forced backwards off the sealing surface into the housing by compressing the spring, allowing the gas contents to flow out of the cylinder through the outlet. (Fig:1) 5.When the cylinder pressure falls below 1-5 Bar, the spring force closes the piston against the valve seat. Therefore a residual pressure is retained in the cylinder at the end of its discharge cycle. (Fig:2) Gas Passage Closed Gas Passage Opened Cylinder Pressure > 7.5 Bar Cylinder Pressure 1-5 Bar Fig:2 Fig:1

Application Specification and Usage International standard for main valve - ISO 10297:2006 International standard for RPV - ISO 15996:2008 Widely used in developed countries. In Europe almost 80% of all gas cylinder valves are RPV’s. In India, preferred by major gas companies for Inert gas services and in use for last 4-5 years. RPV’s are available for a wide variety of gas service like Oxygen, Inert gases, Hydrogen, Carbon dioxide and gas mixtures and suitable for use up to 300 Bar Working Pressure. RPV’s certified to International standards are available in India with PESO approval.

Types of RPV Offline Outlet is offset with respect to the inlet plane and the Residual Pressure unit is backside of the Outlet. * Offline valves can be designed for any outlet connection but must be used for outlet with internal threads and external threaded outlet requiring sealing in the cone. Inline Inline RPV’s have the Residual Pressure unit installed within the outlet of the valve. * Inline valves can only be designed for external threaded outlet requiring sealing on the face. Classification

Types of RPV Valves with Non return function. The RPV unit is generally provided with a Non Return function that protects the cylinder from back flow of fluids into the cylinder from a higher pressure source. These valves require special filling adaptor for filling and evacuation. * Possible with both Offline and Inline version. Valves without Non return function. The RPV device does not require special filling adaptor for filling but only needed for evacuation. * Only possible with Offline version. Variants

Filling Issues Filling Adaptors The filling adaptor involves a projected Pin, built-in to the end connection to overcome the NRV for filling. The filling adaptor may either be designed so that one end is directly fitted into the filling/vacuum Manifold.(Type:1) Alternately one end is built like a valve outlet, and this allows fitment of existing filling connections to be connected to this end. (Type:2) Note- A filling adaptor may not be interchangeable between valves of different manufacturers for the same outlet. Type :1 Type :2

Consideration Considerations for selecting Filling Adaptor (Usually provided by the valve manufacturer) Compatibility with filling line. Compatibility of the filling adaptor if the same filling line is used for filling RPV as well as simple valves? Design including Material, diameter and length of pin Whether pin length is adjustable or not? By how much? Restriction in Flow & Filling time? Can the same filling adaptor be used to fill simple valves? Cost vs. Reliability

Points to Ponder Other considerations Special valve Protection caps and guard for Offline RPV valves – Refer ISO 11117:2008 for Design, Construction and tests. Different filling lines for valves Residual Pressure and Simple Valves. Ensure correct tools are procured and used to open RPV housing to carry out maintenance. (Fig:1) Introduction of check tool to check presence of Residual pressure in the valves before Pre-filling. (Fig:2) Gland Nut & Housing Opening Tool Residual Pressure Checking Tool Fig:1 Fig:2

Final thoughts Conclusions 1)Maximize benefits by choosing the appropriate design and valve type best suited for your application. 2)Consult your valve manufacturer to select most efficient design of filling adaptors best suited for your filling manifold. 3)Invest in training fillers and end users on valve features, benefits and maintenance. 4)Despite the higher cost the technology is far more reliable today and benefits easily and quickly compensate the cost. 5)As end users of high pressure gases become more aware of the benefits of RPV, they will be inclined to prefer suppliers providing cylinder package with superior valving solutions designed to maintain purity and content integrity. 6)If safety is a priority and not lip service, Residual Pressure valves offers the biggest leap in technology to prevent corrosion of cylinders and improving cylinder life.