Confusion about straight run requirement for DP type of primary element (Orifice) with flow conditioner in ISO 5167 :1993

  • Thread starter Shailesh C Patel
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Shailesh C Patel


i have some confusion in iso 5167.

1> If i am not using flow conditioner then my straight run required for beta=0.7 is 14D"?

2> As per clause 7.3 of ISO, flow conditioner will reduce minimum straight run required. However in clause 7.3.1, straight run between fitting to conditioner should be at least 20D and conditioner to orifice should be 22D. so total straight run =20D+ length of conditioner +22D.

then how straight run requirement reduced?

Shailesh C Patel
Please Refer Orifice Meter Constants Handbook E-2 from Singer Meter division Page 120 to 122 which will clarify your doubt. It explained with figures and graph and the fittings after which orifice installation is required.

The flow conditioners mentioned in clause 7.3.1 is clearly applicable to straight runs calculated to be LONGER than 20D and 22D. I just wonder how you were able to achieve 14D, but with that kind of straight run you should not be requiring a flow conditioner. You only use a flow conditioner when your calculations result to 100D or something, which is not good for your application.