Double Ported Valves

The term port applies strictly to the area of opening of the steam passage where it emerges upon the valve seat. The term steam passage includes the full length of the opening from the cylinder bore to the face upon which the valve is seated.

A double ported steam port is one in which there are two openings or steam ports, leading into one steam passage.

A double ported valve is one in which there are two ports at each end of the valve. These two ports in some cases admit steam to a single cylinder port, and in others to two steam ports, terminating in one steam passage.

A griddle valve is one that has two or more ports at each end upon a seat that has two or more ports for each steam passage.

Double ported valves are employed in some cases to increase the admission of live steam to the cylinder, and in others to increase the exhaust openings also. The effectiveness of a double ported valve is mainly valuable at the beginning of the stroke, and is especially valuable in cases when the travel of the valve is diminished to hasten the point of cut off, because in such cases the outer edges of the valve do not open the steam port to its full width, and a single port is apt to wire draw the steam. By the employment of more than one port, or several ports, a sufficient admission may be obtained with less valve travel.

The Allen double ported valve is one in which the second port increases the port opening for the admission only, as shown in Fig. 3303, in which the valve is moving in the direction of the arrow; the port k will receive steam through the opening at g, and from a port passing through the valve, the steam entering it as shown by the arrow. The second port forms part of the lap of the valve, and enables the travel to be short enough to be cut off at early points in the stroke, without employing so much steam lap as to widely distort the points of cut off, this latter being a defect of the D valve.

Webb’s patent slide valve is circular, and is so arranged as to be free to revolve in the hoop of the valve rod, the effect being that the valve moves around, or to and fro in the hoop, without any special mechanism to produce such movement, and the result is, that the valve and port facings wear smooth and even without any tendency to become grooved.