A gate valve and a seat insert for a gate valve having a valve body, which may be used for hydrocarbon well fracturing operations with a fracturing fluid, or “frac fluid”, includes a seat pocket for receipt of the seat insert and a seat, which seat insert may include a tubular member having a first and a second seat insert end face, the first and second seat insert end faces each include at least one annular seal, and the seat insert is disposed in the seat pocket with the first seat insert end face sealed against the valve body and the second seat insert end face sealed against the seat.