A Ball Float Valve has four (4) parts:
1. an extractor fitting
2. a threaded metal tube
3. a wire cage
4. a hollow metal ball float
The metal ball is placed inside the wire cage, which is attached to the metal tube is threaded into the extractor fitting. The extractor fitting is threaded into the bung used for Stage I vapor recovery that is mounted on the top of the tank, so that the metal tube, hollow ball and cage assembly are oriented inside the tank.
Any UST that accepts delivery or transfer of product via a tight connect must have a drop tube with an auto shut-off device (e.g. flapper valve) that closes at 95% of tank capacity. If you use a ball float valve with a flapper valve, the ball float valve must be set to close at a capacity that is greater than 95%. Tanks that do not accept a delivery or transfer of product via a tight connect are not required to use an auto shut-off device in the drop tube (e.g. flapper valve). These tanks may use a stand-alone ball float valve. However, the ball float valve must close when the level of product reaches 90% capacity.
When a transfer of product is made to the tank the level of product inside the tank begins to rise. When the level of product reaches the ball float it too will begin to rise. As product continues to be delivered into the tank, the ball float will continue to rise with the product until it is seated against the bottom of metal tube. This prevents any further displacement of vapor from the tank.
A small opening on the side and near the top of the tube allows a small amount of vapor to escape and allows product to rise very slowly inside the tank. This provides the delivery operator with sufficient time to stop the transfer process and allows any product remaining the delivery transfer hose to drain into the tank. These devices must be compatible with the product stored in the tank.