Where can I buy a Boiler Blowdown Valve? At ChemWorld we carry two heavy duty boiler blowdown valves. A good Boiler Blowdown Valve is require to control proper boiler water chemistry. With a Boiler Blowdown Valve you must manually control you water chemistry with manual valves or bottom blowdowns. Use a high pressure Motorized Blowdown Valve to control your chemistry. Use in conjunction with a controller. These two valves come with 1/2" NPT thread and 3/4" NPT Thread.