Compact hydraulically centered three-way transfer valve

A method of operating a transfer valve comprises:

• maintaining a spool of the transfer valve in a centered position, wherein maintaining the spool of the transfer valve in the centered position comprises:
• fluidically connecting a first pressure source to a first control port that is fluidically connected to a first cavity and a first control surface of a spool of the transfer valve;
• fluidically connecting the first pressure source to a second control port that is fluidically connected to a second cavity and a second control surface of the spool;
• uncovering a first centering port and fluidically connecting the first cavity to the first centering port when the spool shifts out of the centered position and when the second control surface moves toward the second control port and when the first control surface moves away from the first control port, wherein the first centering port is fluidically connected to a second pressure source that is lower in pressure than the first pressure source;
• and
• uncovering a second centering port and fluidically connecting the second cavity to the second centering port when the spool shifts out of the centered position and when the first control surface moves toward the first control port and when the second control surface moves away from the second control port, wherein the second centering port is fluidically connected to the second pressure source.

A transfer valve comprising:

• a housing extending axially from a first end to a second end along a center axis of the transfer valve;
• a spool in the housing, wherein the spool comprises:
• a first control surface facing toward the first end of the housing;
• and
• a second control surface facing toward the second end of the housing;
• a first cavity in the housing and axially between the first control surface and the first end of the housing;
• a second cavity in the housing and axially between the second control surface and the second end of the housing;
• a first control port axially between the first end of the housing and the first control surface and extending through the housing to fluidically connect to the first cavity;
• a second control port axially between the second end of the housing and the second control surface and extending through the housing to fluidically connect to the second cavity;
• a first centering port extending through the housing and axially between the first control port and the second control port;
• and
• a second centering port extending through the housing and axially between the first centering port and the second control port, and
• wherein the spool is configured to block and close the first centering port and the second centering port in a centered position of the spool, and
• wherein the first centering port is fluidically connected to the first cavity or the second centering port is fluidically connected to the second cavity when the spool is not in the centered position.