Single Piston & Double Piston Effect Seats on Ball Valves
SPE (Single Piston Effect) seats are usually called self-relieving seats. Trunnion-mounted ball valves with SPE seats are able to release excess pressure in the cavity into the pipeline automatically.
An SPE seat has seals on the back located in a way that the piston force can only come from the pipeline direction. If the cavity pressure of the body exceeds the pipeline pressure (more than 1.33 times the valve pressure rating per ISO/API), the SPE seat will release pressure to the pipeline. An SPE seat will also release body pressure, even if it doesn't exceed the valve pressure rating. But if there is a differential pressure between the pipeline and the body cavity, the latter will be at a higher pressure. The amount of differential pressure that the seat will relieve varies with valve models and manufacturers.
DPE (Double Piston Effect) seats are usually known as bi-directional seats defined by ISO 14313/API 6D.
A DPE seat is a special seat design, with the location of seals on the back of the seat being located in a way that the seat can use pressure from either the pipeline or the valve cavity to provide a piston force. With the DPE seat option, if leakage occurs in the valve upstream, the pressure entering the body cavity will push the seat downstream against the ball and the seal. Pressure in the line forces the floating seat to achieve seal.
DPE seated valves must have an external relief valve fitted to the body which can be vented to the atmosphere. Due to environmental requirements, this must now be plumbed back into the side upstream of the valve or recycled elsewhere.
An SPE seat has seals on the back located in a way that the piston force can only come from the pipeline direction. If the cavity pressure of the body exceeds the pipeline pressure (more than 1.33 times the valve pressure rating per ISO/API), the SPE seat will release pressure to the pipeline. An SPE seat will also release body pressure, even if it doesn't exceed the valve pressure rating. But if there is a differential pressure between the pipeline and the body cavity, the latter will be at a higher pressure. The amount of differential pressure that the seat will relieve varies with valve models and manufacturers.
DPE (Double Piston Effect) seats are usually known as bi-directional seats defined by ISO 14313/API 6D.
A DPE seat is a special seat design, with the location of seals on the back of the seat being located in a way that the seat can use pressure from either the pipeline or the valve cavity to provide a piston force. With the DPE seat option, if leakage occurs in the valve upstream, the pressure entering the body cavity will push the seat downstream against the ball and the seal. Pressure in the line forces the floating seat to achieve seal.
DPE seated valves must have an external relief valve fitted to the body which can be vented to the atmosphere. Due to environmental requirements, this must now be plumbed back into the side upstream of the valve or recycled elsewhere.
