Abstract: A straightway valve for a positive-displacement machine comprises a polyhedral body with outlet ports and seat surfaces on the sides thereof, flat friction-free closure plates, and a means for attachment of the closure plates to the body, which takes the form of a polygon-shaped plate having on its ends clamping lugs for holding the closure plates in place on the seat surfaces of the body. The polygonal plate has, for example, a bore with projections formed around the periphery thereof and engaging a blind recess in the end face of the body, thus providing for a reliable and easily removable attachment of the plate to the valve body. The valve can serve as a suction and delivery valve in cylinders for compressors of any output with pressures of up to 1,500 kg/cm.sup.2 and with shaft rotational speeds of up to 3,000 revolutions per minute.