Compact-type valve sets new standards:
Robust electropneumatically driven seat valves

In mechanical and plant engineering space is at a premium. Therefore Buschjost has reduced the valve function to a minimum for the new compact, electropneumatic 84 80/84190 valve series, without having to sacrifice safety, reliability and functionality. The series has been tailored to meet the concerns of mechanical and process engineering.

Liquid and gaseous fluids, such as steam, cleaning agents, compressed air or vacuum are mandatory in most of these production lines. They must be available exactly in time with the machines to the very second. At the same time the design engineers have the task of arranging the leads and valves so that they take up less and less space. Against this background, Buschjost has developed the new, extremely compact series of valves with electropneumatically and pneumatically driven valves from the 84180/84190 series. Even under the most cramped installation conditions they can still be fitted into machines and plants. The company paid special attention to the various fields of application in mechanical engineering, packaging technology and to the auxiliary processes in the pharmaceuticals and food industries.

Apart from the compact design, a high performance pneumatic drive system was also important. It can be controlled both by a valve terminal and by means of a small 3/2-way solenoid valve directly connected to the drive.

Picosol for 50 million switching operations

In order to then develop an electropneumatic valve from a pneumatic one, a control valve is required. In the past these were rather voluminous in shape. The Buschjost sister company, FAS, has produced the Picosol, a control valve with a construction height of only 19 mm, for the new valve series (84180/84190). The electromagnetically actuated 3/2-way pilot valve and the seat valve together are only 84 mm high.

Nevertheless the Picosol is in no way inferior to its “big” predecessors in terms of performance, reliability and speed. The control valve produced from high quality PPS plastic works very fast. It responds within 8 – 15 ms and controls the main valve reliably. Its qualities have been proved in comprehensive test series with 50 million switching operations.

Straight-seated valve with short stroke

In view of the fact that the system was a completely new design and not an improvement of an existing series, the developers did not need to make any allowance for existing technical specifications; they were able to set out to find the optimum. Of course, it must be mentioned that in valve technology the search for the optimum does not mean an absolute optimum; it is always the search for the best compromise. Establishing a ranking for the optimisation parameters was one of the first steps. Since the top priority on the agenda was the compact design, the remaining items had to bow to this. The only exception was the exacting quality standard, which of course comes first.

The result of this development was a multipurpose series of valves (84180/94190), which is designed as directly-controlled straight-seated valves and is available in the sizes G1/8 and G1/2. The external dimensions alone speak for themselves. In all versions the valves, including the pneumatic drive, measure only 65 mm and, together with the electropneumatic drive, only 84 mm in height. The high torque drive requires only a space with a 33-mm diameter.

Versions in stainless steel and brass are available to enable the valves to be used for multiple purposes. They work reliably in the range from -0.9 to 4 bars and control a temperature range between -10 and +90 degrees. The short-stroke valves are designed for up to 3-5 million cycles and are therefore also suitable for dosing. Furthermore, they are excellently finished, enabling maintenance-free operation.

In the case of the straight-seated valves a valve disk is pressed form- and force-closed onto the geometrically matched valve seat and seals the valve. Owing to their design, these valves have a number of advantages. They are not susceptible to dirt and calcification and are very suitable for neutral to aggressive liquid and gaseous media. Their closing and opening movements run a linear course. They can reliably shut off media at higher temperatures and higher pressures and have long service lives. The characteristics of seat valves are largely determined by the execution of the seat, the design of the sealing elements and the valve body.

For Buschjost this means that all relevant parameters are very exactly analysed beforehand and elaborately optimised using state-of-the-art design simulation tools. Undesired turbulences, laminar and turbulent flows can be traced, analysed and reduced to an optimal level using these tools. Since for this project the realisation of a compact structure was at the top of the list, the developers paid special attention to such factors as the size of the boiler, seat diameter, stroke heights and angles of incidence.

Roller-burnished and smooth

The right choice of surface finishing is also part of optimisation. Hence the important components of the valves (84180/84190), such as spindles and the inner area of the drive, have very smooth, roller-burnished surfaces. It is not least of all these spots that determine how long a valve will function. The better the quality of the finish of the spindle surfaces which run in ring seals and gland seals, the lower the amount of wear and the longer the service life will be.

Another important point is the conception and selection of the seals. Modern, self-adjusting gland seals such as those used in the new valve series show their strong features at high temperatures and with aggressive fluids, which they control reliably. For such purposes seals made from PTFE, FPM or EPDM are used.