LESER has standardized the balanced piston for the API safety valve and offers this option now for all nominal sizes of this type. This accessory can be used for the complete application range of the API series with bellows design.


The purpose of the additional balanced piston is to ensure the back pressure compensation even in case of failure of the bellows and to further assure the temperature screening to the spring room. This means that the balanced piston is without effect as long as the back pressure compensating bellows is intact. Only if the bellows fails there will be pressure at the piston. The surfaces of the piston and of the seat section are of almost equal size, generating this back pressure compensating effect. However, the balanced piston does not seal towards the bonnet space and does consequently not protect the moving parts from corrosion or dirty media.

In case of valve bodies made of standard material such as WCB, LCB, CF8M and WC6, all components of the piston are made of stainless steel 1.4404/316L. Other material can be selected according to the API Alloy Concept via the special process.
Body to bonnet bolting is adapted to the ASME Standard and are made of the materials B7/2H and B8M/8M. For CE or EAC conformity it is necessary to change the studs and nuts.

This new accessory can only be selected via option code K10 for API safety valves with bellows. The standard delivery time of a safety valve with balanced piston is ten weeks.

The balanced piston is a solution which is included in API 520. Especially the oil company Saudi Aramco equips its bellows valves regularly with this valve configuration. But also other customers specify the balanced piston for highly critical applications when a back pressure compensating function must be guaranteed in any case. Altogether, we have already successfully completed a multitude of orders with several hundred valves with the accessory balanced piston.