Balanced valve trim and method of reducing stem forces on a valve stem

A valve, comprising:

• a valve body defining a fluid flow path extending from an inlet to an outlet;
• an orifice with a flow passage defined by an inner wall surface extending from an orifice inlet to an orifice outlet, wherein the inner wall surface of the orifice defines a converging section, a diverging section, and a vena contracta between the converging section and the diverging section;
• a valve seat disposed along the converging section of the inner wall surface;
• and
• a valve plug that reciprocates linearly into the converging section to control the flow of fluid through the flow passage and the fluid flow path,
• wherein the valve plug comprises a body portion extending from a back end to a tapered nose portion that seats against the valve seat, the tapered nose portion has a tip at a distal end, and a balance port extends through an outer surface of the tapered nose portion, wherein the balance port is vented through the valve plug to equalize a first pressure along the tapered nose portion with a second pressure at the back end of the valve plug body, and wherein the balance port is spaced apart from the tip;
• a shoulder at a junction of the body portion and the tapered nose portion, wherein the outer surface of the tapered nose portion extends from the shoulder to the tip;
• and
• wherein the balance port is disposed between the shoulder and the tip, the balance port spaced a first distance from the shoulder and a second distance from the tip, the second distance being greater than the first distance.

A valve trim for a flow control valve, comprising:

• an orifice with a flow passage defined by an inner wall surface extending from an orifice inlet to an orifice outlet, wherein the inner wall surface of the orifice defines a converging section, a diverging section, and a vena contracta between the converging section and the diverging section;
• a valve seat disposed along the converging section of the inner wall surface;
• and
• a valve plug that reciprocates linearly into the converging section to control the flow of fluid through the flow passage,
• wherein the valve plug comprises a body portion extending from a back end to a tapered nose portion that seats against the valve seat, the tapered nose portion has a tip at a distal end, and a balance port extends through an outer surface of the tapered nose portion, wherein the balance port is vented through the valve plug to equalize a first pressure along the tapered nose portion with a second pressure at the back end of the valve plug body, and wherein the balance port is spaced apart from the tip;
• a shoulder at a junction of the body portion and the tapered nose portion, wherein the outer surface of the tapered nose portion extends from the shoulder to the tip;
• and
• wherein the balance port is disposed between the shoulder and the tip, the balance port spaced a first distance from the shoulder and a second distance from the tip, the second distance being greater than the first distance.

A method of reducing stem forces on a valve stem of sliding stem valve having a flow control orifice defined by an inner wall surface extending from an orifice inlet to an orifice outlet, wherein the inner wall surface of the flow control orifice defines a converging section, a diverging section, and a vena contracta between the converging section and the diverging section, a valve plug coupled to the valve stem and arranged to reciprocate linearly toward and away from a valve seat disposed along the converging section of the inner wall surface of the flow control orifice, wherein the valve plug has a body portion extending from a back end to a shoulder at a junction of the body portion and a tapered nose portion, the tapered nose portion extending from the shoulder to a tip, the method comprising:

• directing a flow of fluid between the valve plug and the inner wall surface of the flow control orifice such that the tip of the valve plug is on the downstream side of the valve plug;
• forming a throat between an outer surface of the valve plug and the inner wall surface of the orifice, wherein the throat is located along the tapered nose;
• and
• equalizing a first pressure at the back end of the body portion with a second pressure at a point located between the throat and the tip of the valve plug by venting a fluid through a balance port extending through the outer surface of the tapered nose portion, wherein the balance port is spaced a first distance from the shoulder and a second distance from the tip, the second distance being greater than the first distance.