What solutions are recommended when faced with space problems?
Several solutions exist to reduce the total straight length necessary for the purpose of installing a differential pressure flowmeter. Here is a non-exhaustive list of these solutions:
1. Flow straightener / conditioner: this item considerably reduces the disturbances caused by the upstream accessory and thus improves the measuring accuracy and reduces the required straight lengths. The characteristics of these devices are described and listed in the ISO5167 standard. See question above for an estimation of the reduction in straight length.
2. Multi-hole plate: this is the economical solution for reducing upstream and downstream straight lengths. Indeed, a minimum distance of 2xD (upstream and downstream) is recommended between the primary element and the pipe fittings. This DP element has been the subject of extensive experiments and is already used in many applications but it is not standardized to date.
3. Venturi tube: this device has a particular geometry that helps to reduce the irregularities of the flow; thus, the required straight lengths are reduced compared to an orifice plate for example (for β = 0.5 and a simple 90 ° elbow upstream, the straight length required for an orifice plate is 22xD while is 9xD for a venturi tube). Its price is however higher than an orifice plate.
4. Cone meter: the straight lengths required to install a cone meter are reduced (3xD upstream and 2xD downstream). But the uncertainty on the discharge coefficient is 5% while it can reach 0.5% for an orifice plate. A specific calibration can be proposed to improve the measurement accuracy.
Each of the characteristics of your process is to be studied to choose the best solution in terms of measurement quality, size and price. That is why we are at your disposal to provide you with additional information and help you in your selection.