Control.com - Nerds in Control

Can anybody tell what is the practical significance of orifice beta ratio between 0.3 to 0.7? What will happen if beta ration goes below 0.3 or goes above 0.7?

Beta Ratio is the ratio between the line inner diameter to bore size of the orifice. The flow coefficient is found to be stable between beta ratio of 0.2 to 0.7 below which the uncertainity in flow measurement increases.

Interesting question. I don't have all the books and material at hand now to give a very detailed answer. However, I will try to throw some light on it off my head.
1. Orifice plate flow calculation formula is basically based on empirical formulas based on actual testing. Most of the results are available for beta ratio 0.3 to 0.7.
2. Low beta ratio means the plate has a smaller hole i.e pressure loss will be higher. This may cause higher size of pump and more money.
3. Higher beta ratio increases the discharge coefficient uncertainty. Higher beta ratio means low differential pressure across your orifice and some times may be difficult to measure.
4. Higher beta ratio needs longer staright length.

I remember long time back when we used to do manual calculations of orifice plate bore as per BS 1042, we always tried to keep the beta ratio approx. 0.6. Because near to o.6 beta ratio the discharge point curve is almost flat, so that even if there is some mistakes in your manual calculation, overall accuracy is not affected.

Hope this helps a little!

thanks for the reply.