A rotary valve, comprising: a valve body and an adapter coupled to one end of the valve body, thereby defining a valve inlet, a valve outlet, and a valve interior in fluid communication with the valve inlet and the valve outlet; a valve stem disposed in an opening of the valve body and partially disposed in the valve interior; a floating ball element pivotably mounted in the valve interior via the valve stem to control fluid flow between the valve inlet and the valve outlet; a first valve seat movably disposed in the valve interior proximate to the valve inlet, the first valve seat biased toward the ball element to sealingly engage a first portion of the ball element; and a second valve seat removably disposed in the valve interior proximate to the valve outlet and configured to sealingly engage a second portion of the ball element, wherein the second valve seat is clamped between a surface of the valve body and a surface of the adapter, wherein the adapter includes a circumferential recess and an annular shoulder defined at a position radially outward of the recess, and wherein the second valve seat comprises a substantially annular body and a skirt extending outwardly from the substantially annular body, the skirt arranged within the recess formed in the adapter, the rotary valve further comprising: a gap formed between the one end of the valve body and the annular shoulder of the adapter; and a sealing element arranged between the valve body and the adapter to prevent leakage to atmosphere via the gap. a valve body and an adapter coupled to one end of the valve body, thereby defining a valve inlet, a valve outlet, and a valve interior in fluid communication with the valve inlet and the valve outlet; a valve stem disposed in an opening of the valve body and partially disposed in the valve interior; a floating ball element pivotably mounted in the valve interior via the valve stem to control fluid flow between the valve inlet and the valve outlet; a first valve seat movably disposed in the valve interior proximate to the valve inlet, the first valve seat biased toward the ball element to sealingly engage a first portion of the ball element; and a second valve seat removably disposed in the valve interior proximate to the valve outlet and configured to sealingly engage a second portion of the ball element, wherein the second valve seat is clamped between a surface of the valve body and a surface of the adapter, wherein the adapter includes a circumferential recess and an annular shoulder defined at a position radially outward of the recess, and wherein the second valve seat comprises a substantially annular body and a skirt extending outwardly from the substantially annular body, the skirt arranged within the recess formed in the adapter, the rotary valve further comprising: a gap formed between the one end of the valve body and the annular shoulder of the adapter; and a sealing element arranged between the valve body and the adapter to prevent leakage to atmosphere via the gap. a gap formed between the one end of the valve body and the annular shoulder of the adapter; and a sealing element arranged between the valve body and the adapter to prevent leakage to atmosphere via the gap.