THF casing back pressure valve suits to cementing operation in gas and oil drilling. While cementing, the tool can prevent the mud from backflowing into casing, which serves as a single valve. it is an useful tool to improve cementing quality. our company produces all kinds of casing back pressure valves,including common specification 4 1/2", 5",5 1/2". we can also design and manufacture the product according to customers' requirement.