We do both. The Burrell whistle is a genuine 1/2 size whistle with valve, the 1/2 size siren's will require a whistle valve.
You can find these on our website,
www.heritagesteamsupplies.co.uk
Any questions, call me on 07785 258169
SG
Actually I just checked, the 1/2" burrell whistle is not on our website as yet. I will post a picture today.
SG