Precision On Flow Coefficients Is Essential Throughout Valve Manufacturing

The oil and gas valve manufacturing sector is almost entirely ruled by strict internationalised standards but the flow coefficient estimates quoted by many firms is a notable exception to this rule, as Paul Shillito explains.

The extraction, transportation, and refining of oil and gas is – for obvious reasons – a process that demands high levels of engineering precision.

As every valve manufacturer knows, the industry is regulated using a long list of internationally-accepted standards that govern a wide range of parameters. These include, among others, pressure and temperature ratings, seat tightness and the face-to-face dimensions of units.

However, one area without this regulation is the flow coefficient (Cv) of a valve -  which measures how efficiently fluid can flow (through a valve).

Despite flow coefficient testing is relatively simple, it’s up to manufacturers to decide how they calculate the figures for their valve specification sheets and, they are under no obligation to state their methods unless a customer requests it.

The issue here is the potential discrepancies between the figures quoted for valves of similar sizes and designs, with many estimated valves being entirely unconvincing.

Significant Risk To Projects

Flow coefficients are the main metrics used to select valves of the right size for any given purpose. An error in judgement here can be both expensive and highly inconvenient. Take a valve that is too small, for example, and be potentially faced with the problem of restrictions when it comes to allowing fluid to flow through. This mistake can potentially cause a wide range of issues both upstream and downstream, especially when the effect is compounded across multiple units, all with inaccurately stated values.

If an engineer makes specifications on delivering a certain Cv value, but the actual valves supplied fall short of this, then this is unlikely to be noticed until the system is commissioned. At this point, having to go back and replace valves would be a significant blow in terms of project budget and timeframes.

Gunning For Standardisation In Valve Manufacturing

At Oliver Valves, we have carried out testing programmes for a number of different valves to accurately determine their flow coefficients. Our valve manufacturing processes are carried out in partnership with various test houses. The larger bore valves being run at E.ON Ham’s Hall calibration facility near Birmingham, UK and, of course, while this involved financial investment, the confidence it has provided us made it worthwhile.

Overall, there is a strong argument for standardisation internationally. It doesn’t make sense that so many other aspects of valve production are stringently standardised, and yet there is apparently no regulation over quoting Cv values, which stands as a key aspect of valve performance.