Simply Koi and More Koi

I want to fit a air pressure relief valve and wanted to now if it`s one size fits all size air pumps and is it better to use 2 relief valves ??

thanks.

See here ... air pressure releif valve (mid way down the page) ... http://www.koicarp.net/air_products/airpumps/secoh.html" onclick="window.open(this.href);return false;

one should be enough per pump ... used as a safety feature. If after fitting, it keeps venting - you might want to consider using a smaller more appropriately sized pump or adding more outlets/airstones etc.