Friday, December 22, 2017

Combining Rupture Discs With Pressure Relief Valves

rupture disc
Applying a rupture disc in concert with a safety relief
valve can deliver real benefits.
Image courtesy Continental Disc Corporation
Common elements of any pressurized system include safety and pressure relief valves. Their general purpose is to stop system pressure from exceeding a preset value, preventing uncontrolled events that could result in damage to personnel, environment, or assets. Their operating principle and construction are comparatively simple and well understood.

Long term exposure of a relief valve to process media can result in corrosion, material buildup, or other conditions which may shorten the useful life of the valve, or worse, impair its proper operation. This excessive wear will increase the ongoing cost of maintaining or replacing a prematurely worn valve. One other aspect of relief valves can be the reduction in their seal integrity or force as the system pressure approaches the setpoint. This could possibly lead to fugitive emissions, an undesirable condition.

An effective approach to mitigating some of the effects of exposure to the process media is to install a rupture disc upstream of the safety valve inlet. Isolating a relief or safety valve from the process media through the installation of a rupture disc upstream of the valve inlet will eliminate exposure of the costly valve to effects of the media. It is necessary to establish proper rating and selection for the rupture disc to avoid any impairment of the overall operation of the relief valve, but the selection criteria are not complex. A number of benefits can accrue with this concept.
  • Rupture disc isolates the valve from the media, allowing application of less costly valves fabricated of non-exotic materials.
  • Rupture discs are leak free and bubble tight, eliminating possibility of fugitive emissions from the safety relief valve, especially when system pressure may approach valve setpoint.
  • Relief valve inventory can be evaluated for reduction.
  • Longer valve life.
  • Less downtime.
The additional cost for the rupture disc enhancement can have a reasonable payback period, with all factors considered. In any case, the rupture disc protection makes for a cleaner relief valve installation. The document provided below provides some additional application recommendations and details.

Rupture discs and holders are available in sizes and materials for most applications. Share your ideas with a product specialist, combining your process knowledge with their product application expertise to develop an effective solution.


Thursday, December 7, 2017

Quarter Turn vs Linear Valves

fully lined ball valve
This lined ball valve is an example of a
quarter turn valve.
Image courtesy Flowserve - Atomac
Different types of valves are designed and applied for different roles in the process control. Linear valves and quarter-turn valves are two different types of valves utilized throughout industry to regulate and control fluid flow. Their design and construction reflect the intent of the valves’ application, with each being suited for a different class of use.

All valves operate by providing control of the position of an internal structure that impedes fluid passage to some degree. Generally, fluid flow at the valve can be characterized as one of three conditions, unrestricted (valve fully open), stopped (valve fully closed), and throttled (valve partially open). Process operational requirements will dictate whether just two (fully open and fully closed) or all three of those conditions will be needed. Many aspects of the fluid, the process, and the surrounding environment come into play when making an appropriate valve selection. Not always an easy task.

Linear valves are generally characterized by their straight line motion that is used to position the valve plug, disc, diaphragm or other flow controlling element. The shape, size, and arrangement of the linear valve trim is generally intended to empower the operator with a range of flow through the valve. Through its positioning, the linear valve is able to regulate fluid flow at a slower, but more accurate rate. The valves can move a disk or a plug into an orifice, or push a flexible material, such as a diaphragm, into the flow passage. Gate valves and fixed cone valves are common examples of linear motion valves. Linear valves are best applied as flow controllers, and are often suited for frequent operation and repositioning.

Quarter turn valves traverse from fully open to fully closed by a 90 degree rotation of a shaft connected to the controlling element. Their comparatively simple operation allows for a design that is rugged and compact. One distinction of the quarter turn valves is their ability to quickly reposition from open to closed positions. Torque requirements to operate the valves are generally low to moderate. Ball and butterfly valves are examples of quarter turn valves.

Depending on the specific scenario, linear valves and quarter-turn valves are optimal choices for particular process environments. The accuracy of the linear valve and its ability to move in a linear fashion as opposed to a quarter-turn comes coupled with easy maintenance and decreased likelihood of cavitation. Both valve types enjoy widespread use and should generally not be viewed as competing designs for the same application. Each has a range of applications where it excels.

Share your fluid flow control challenges of all types with valve specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.