Cover, fluid end and plunger pump

A fluid end, comprising a cover, wherein the cover comprises:

• a body, the body being cylindrical, and the body comprising a first end, a second end, and a side surface connecting the first end of the body and the second end of the body;
• a main flow channel extending along an axis of the body;
• a plurality of subsidiary flow channels, each of the plurality of subsidiary flow channels being communicated with the main flow channel;
• a first opening located at the first end of the body and communicated with the main flow channel;
• a plurality of second openings located at the side surface of the body, each of the plurality of subsidiary flow channels being communicated with at least one of the plurality of second openings;
• a drain channel with a first end and a second end, a first drain outlet located at the first end of the drain channel, and a second drain outlet located at the second end of the drain channel, wherein the first drain outlet is located at the side surface of the body, and the second drain outlet is located at an end surface of the second end of the body;
• and a first sealing groove and a second sealing groove, wherein the first sealing groove is configured to receive a first sealing ring, the second sealing groove is configured to receive a second sealing ring, the first sealing groove and the second sealing groove are both located at the side surface, and the first drain outlet is located between the first sealing groove and the second sealing groove.