Major valve parts include two types of functions one namely pressure-retaining which includes a valve body, bonnet or cover, Cover bolting, Disc, and the other major non-pressure retaining parts of a valve, like a valve seat(s), stem, yoke, packing, gland bolting, bushings, handwheels, valve actuators, etc.
What is Valve Trim?
The trim, particularly the mating elements that regulate the stream to the controller’s demands, is at the heart of the control valve. Each process is distinct in its own right, necessitating particular flow control features. Valve trim includes the stem, plug, disc, seating surface, etc. It’s also the plug and seat arrangement’s actual shape.
| Type of Valves | Valve Trims |
| Angle Valves | Stem, Seat, Disc, Disc nut, back-seat bushing |
| Gate Valves | Stem, Seat, Wedge, back-seat bushing |
| Globe Valves | Stem, Disc, Seat, Disc nut, back-seat bushing |
| Disc Valves | Disc, Disc nut, back-seat bushing |
| Lift type check valves | Seat ring, Disc, Disc guide |
| Swing type check valves | Seat ring, Disc, Disc nut, Disc nut pin, Disc holder, Disc holder pin, side plug, carrier pin |
Valve Trim Parts
- DISC
- The disc is a part of the valve which allows, throttles, or stops flow depending on its position it is a pressure-retaining part of the valve. Types of disc present on the valve define the name of the valve. over plug or ball valve the disc is called a plug or ball. A disc will be seated against the stationary valve seat or seats when the valve is in the closed position, during the closed position the disc performs a pressure-retaining function whereas during the valve open position the disc doesn’t perform the pressure-retaining function. It can be moved away from valve seats by the motion of the valve stem, except in the check and safety relief valves the disc is moved away from its seats by fluid flow and pressure. A valve disc is usually cast, forged, or fabricated.
- SEAT
- A valve seat is one of the non-pressure retaining parts of the valve. Valves will be having maybe one or more than one seat, as in the cases of globe or swing check valve, there will be one seat forming a seal with the disc to stop the flow. Whereas for the gate valve there will be two seating surfaces that will come in contact with the seats. Likewise, plug and ball valves, depending upon the number of ports will have several seats. Valve seats can be integral, renewable, or replaceable rings. Small valves are provided with screwed-in, swaged-in, or welded valve seats, and in big valves, they may have any of the seats used in small valves and they will have integrally cast or forged seats along the valve body.
- Back Seat
- The back seat comprises a shoulder on the stem and a mating surface on the underside of the bonnet. When the stem is entirely open, it forms a seal. It inhibits media leakage into the packing chamber and into the environment. Note: For safety reasons, it is NEVER recommended to change the packing while the valve is under pressure.
- STEM
- The stem connects the actuator, valve handwheel, and the disc, plug, or ball. Required for the opening and closing of the valve motion. Thus, the motion of the stem opening and closing of the valve took place. In a gate or globe valve linear motion of the disc is needed to open or close the valve. Whereas in the plug, ball, and butterfly valve the valve disc is rotated to open or close the valve. Stop check valves and check valves do not have any stem.
API600 Valve Trim chart
The API600 trim chart specifications are designed for API600 gate valves. For API603 gate valves as well as globe valves and check valves, the same trim numbers are more loosely applied (Trim Chart not referenced in latest API603 Standard). Obviously, in regard to globe and check valve, the hardness differentials shown on the disc and seat are specified for gate valves subject to more wear, gauling, sticking etc., and not as relevant. Also, globe and check valves are often specified to BS (now ISO) specifications. API 623 for globe valves and API594 for swing check valves is now used in lieu of obsolete BS 1868 and BS 1873
| API Trim No. | Material | Seat | Disc | Backseat | Stem | Notes |
| 1 | 410 | 410 | 410 | 410 | 410 | |
| 2 | 304 | 304 | 304 | 304 | 304 | |
| 3 | F310 | 310 | 310 | 310 | 310 | |
| 4 | Hard 410 | Hard 410 | 410 | 410 | 410 | Seas 750 BHN min. |
| 5 | Hardfaced | Stellite | Stellite | 410 | 410 | |
| 5A | Hardfaced | Ni-Cr | Ni-Cr | 410 | 410 | |
| 6 | 410 and Cu-Ni | Cu-Ni | Cu-Ni | 410 | 410 | |
| 7 | 410 and Hard 410 | Hard 410 | Hard 410 | 410 | 410 | Seas 750 BHN min. |
| 8 | 410 and Hardfaced | Stellite | 410 | 410 | 410 | |
| 8A | 410 and Hardfaced | Ni-Cr | 410 | 410 | 410 | |
| 9 | Monel | Monel | Monel | Monel | Monel | |
| 10 | 316 | 316 | 316 | 316 | 316 | |
| 11 | Monel and Hardfaced | Stellite | Monel | Monel | Monel | |
| 12 | 316 and Hardfaced | Stellite | 316 | 316 | 316 | |
| 13 | Alloy 20 | Alloy 20 | Alloy 20 | Alloy 20 | Alloy 20 | |
| 14 | Alloy 20 and Hardfaced | Stellite | Alloy 20 | Alloy 20 | Alloy 20 | |
| 15 | 304 and Hardfaced | Stellite | Stellite | 304 | 304 | |
| 16 | 316 and Hardfaced | Stellite | Stellite | 316 | 316 | |
| 17 | 347 and Hardfaced | Stellite | Stellite | 347 | 347 | |
| 18 | Alloy 20 and Hardfaced | Stellite | Stellite | Alloy 20 | Alloy 20 |
Importance of Valve Trim design
The trim plays an important role in the characteristics of the valve. It determines the flow rate and the isolations of the valves. The shapes of the valve trim determine the flow characteristics of the valve. A valve trim’s characteristic is related to the percentage of flow and the valve stem travel between 0% and 100%.
Trim materials sometimes are the same material as the valve body or bonnet and sometimes they differ. As per the different properties, required for the components to withstand particular forces and conditions. so that they are constructed of assorted materials. when suitable trim materials are selected, the Flow-medium properties like chemical composition of the fluid, pressure, temperature, flow rate, velocity, and viscosity of the fluids are considered.
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