The Vienna horn uses a unique form of double-cylinder valve associated with the Viennese firm Uhlmann of the 1840s known as a pumpenvalve. A pumpenvalve is similar to the standard piston valve, but it is not pushed directly inward. Instead, long push-rods reach across to each lever key (as with rotary valves), allowing either a fast or slow change in the valve, by lever speed. The pumpenvalve allows the air to flow straight when the valves are not actuated. When a valve is engaged, each cylinder redirects the air stream 90 degrees in one bend, lessening the resistance felt by the player. This type of valve is one of the many contributing factors to the liquid legato that is one of the trademarks of the Viennese school. However, the indirect linkage between the fingers and the valves can make the action slower and therefore make quick technical passages more difficult for the player.