The Delta Faucet Monitor Series is equipped with a stainless steel pressure balancing spool. This pressure balancing unit protects the user by equalizing the water pressure inside of the shower valve itself. This protects the user if there is a decrease in pressure from the hot or the cold supply. If that were to occur the faucet will automatically readjust the water pressure from the opposite side so that it is equal with the supply that dropped in pressure. Meaning that if someone is in the shower and the toilet is flushed, the valve will reduce the hot water pressure coming into the faucet to match the cold. This ensures a scald free environment and a constant temperature within + or - 3 degrees Fahrenheit.
If you always have large differences between hot/cold water pressures, then the faucet will only allow the minimum amount of pressure through. If you have a hot water supply of 25 pounds per square inch and a cold water supply of 60 pounds per square inch then the faucet will always operate at 25 pounds per square inch.