Under certain atmospheric conditions, a film of ice will form on the inside wall of the steam chest. This film prevents the valve from seating properly and also reduces friction between the valve and steam chest wall. In some driving conditions, this lack of friction will allow the valve to “bounce” or “flutter,” needless to say, causing poor performance of the hammer. A quick remedy is the spring arrangement shown in the drawings above left. The spring holds the trip over center as it rotates. A permanent solution to flutter is shown in the drawing above right. This drawing is of the new type trip and open steam chest head equipped with a detent spring.