Email: - Phone: 610-666-1220

bag tanks 2

ASME Bladder Type Thermal Expansion Tanks

In contrast from diaphragm tanks, bladder tanks completely enclose the water inside a replaceable butyl rubber bladder (other bladder materials available upon request), eliminating problems such as water-logging and tank corrosion.  Air precharge pressure is maintained using a car-tire type valve, also known as a Schrader valve.

Thermal expansion can cause pressure build up in domestic water systems.  Thermal expansion tanks are designed to absorb the increased volume of water created by thermal expansion and return it to the system when the hot water is demanded.  This helps protect the system from pressure build-up by keeping the maximum pressure below the relief valve setting.

Similar to other items in a heating or cooling system, bladder tanks must be maintained to ensure proper operation.  Precharge pressure must be field adjusted per the operating conditions of the system it is being installed in.  See IOM for more details regarding proper maintenance procedures.


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The John Wood Company, LLC

Phone (610) 666-1220
Fax (610) 666-0193
Toll Free (800) 537-5581

Remit To:

The John Wood Company
PO Box 644250
Pittsburgh, PA 15264

Mail to:

The John Wood Company
PO Box 364
98 Highland Avenue
Oaks, PA 19456

Ship To:

The John Wood Company
Highland Business Park
98 Highland Avenue
Oaks, PA 19456-1052

NOTE: We are NOT affiliated with the John Wood Water Heater Company of Canada. They may be contacted at 1-888-599-2837, e-mail at or at