Routing underground pipework for a DN350 compressed air pipeline @10-13bar. I need to install several isolation valves along its length. Firstly what type of valve would you reccomend?
I have been advised that a ball valve would be most suitable, does anyone know of any suppliers (UK & Europe) that manufacture ball valves at this size?
A ball valve would work very well. There are several manufacturers that make them this large, and the price will be relatively high.  An internet search under large ball valves will get you different suppliers.  For UK and Europe, Neles, Jamesbury, PBV come to mind. A gate valve will also work but is more likely to leak and you will have the issues with a rising stem underground.  My recommendation is to look at a high-performance butterfly valve.  Tight shut-off, less torque to operate, less cost, and is more readily available.

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