VALVE Body-Bonnet Design TRIM

The word “trim” is often overheard when valve professionals are talking about industrial gate valves. Trim has nothing to do with how slim and fit a valve is, rather it refers to the internal components of a valve that are exposed to great stress or subject to a harsh combination of erosion and corrosion. In a gate valve the trim components are the stem, disc seating area, body seats and backseat, if applicable. Common utility bronze or brass valves usually have trim parts of the same material as the body and bonnet. Cast and ductile iron valves have either all iron trim components or occasionally bronze trim. The term for an iron valve with bronze trim is “iron body, bronze mounted” or IBBM for short.
Because of their weldability, steel valves can be furnished with a number of different trims. Stellite, Hastelloy, 316ss, 347ss, Monel, and Alloy 20 are some of the materials regularly used for gate valve trim.

During most of the 19th century, valves were predominantly supplied with screwed end connections, even in sizes as large as 12” NPT. Since that time the flanged end connection has become the most popular. Other end connection types in use today include screwed, ring-type-joint (RTJ), Victaulic, Greyloc and water works “mechanical joint”.

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2 Responses to “VALVE Body-Bonnet Design TRIM”

1. aliaswn Says:
September 10th, 2007 at 11:01 pm

Valve assembly comprising a valve base, a valve bonnet attached thereto, a rotatable valve stem extending coaxially through the valve bonnet, a rotatable valve handle attached to the valve stem and having a plane of rotation which is generally perpendicular to the axis of the valve stem, and an indicator tab attached to the valve base or the valve bonnet and extending outward from the valve body or valve bonnet in a direction generally parallel to the plane of rotation of the valve handle. The rotatable valve handle can be disposed in at least a first position and a second position, wherein the rotatable handle when disposed in the first position renders the indicator tab invisible when viewed in a direction generally perpendicular to the plane of rotation of the valve handle, and wherein the rotatable handle when disposed in the second position renders the indicator tab visible when viewed in a direction generally perpendicular to the plane of rotation of the valve handle.
2. aliaswn Says:
September 10th, 2007 at 11:02 pm

There is a wide range of safety valves available to meet the many different applications and performance criteria demanded by different industries. Furthermore, national standards define many varying types of safety valve.

The ASME standard I and ASME standard VIII for boiler and pressure vessel applications and the ASME / ANSI PTC 25.3 standard for safety valves and relief valves provide the following definition. These standards set performance characteristics as well as defining the different types of safety valves that are used:

* ASME I valve - A safety relief valve conforming to the requirements of Section I of the ASME pressure vessel code for boiler applications which will open within 3% overpressure and close within 4%. It will usually feature two blowdown rings, and is identified by a National Board ‘V’ stamp.
* ASME VIII valve - A safety relief valve conforming to the requirements of Section VIII of the ASME pressure vessel code for pressure vessel applications which will open within 10% overpressure and close within 7%. Identified by a National Board ‘UV’ stamp.
* Low lift safety valve - The actual position of the disc determines the discharge area of the valve.
* Full lift safety valve - The discharge area is not determined by the position of the disc.
* Full bore safety valve - A safety valve having no protrusions in the bore, and wherein the valve lifts to an extent sufficient for the minimum area at any section, at or below the seat, to become the controlling orifice.
* Conventional safety relief valve - The spring housing is vented to the discharge side, hence operational characteristics are directly affected by changes in the backpressure to the valve.
* Balanced safety relief valve - A balanced valve incorporates a means of minimising the effect of backpressure on the operational characteristics of the valve.
* Pilot operated pressure relief valve - The major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief device.
* Power-actuated safety relief valve - A pressure relief valve in which the major pressure relieving device is combined with, and controlled by, a device requiring an external source of energy.

The following types of safety valve are defined in the DIN 3320 standard, which relates to safety valves sold in Germany and other parts of Europe:

* Standard safety valve - A valve which, following opening, reaches the degree of lift necessary for the mass flowrate to be discharged within a pressure rise of not more than 10%. (The valve is characterised by a pop type action and is sometimes known as high lift).
* Full lift (Vollhub) safety valve - A safety valve which, after commencement of lift, opens rapidly within a 5% pressure rise up to the full lift as limited by the design. The amount of lift up to the rapid opening (proportional range) shall not be more than 20%.
* Direct loaded safety valve - A safety valve in which the opening force underneath the valve disc is opposed by a closing force such as a spring or a weight.
* Proportional safety valve - A safety valve which opens more or less steadily in relation to the increase in pressure. Sudden opening within a 10% lift range will not occur without pressure increase. Following opening within a pressure of not more than 10%, these safety valves achieve the lift necessary for the mass flow to be discharged.
* Diaphragm safety valve - A direct loaded safety valve wherein linear moving and rotating elements and springs are protected against the effects of the fluid by a diaphragm.
* Bellows safety valve - A direct loaded safety valve wherein sliding and (partially or fully) rotating elements and springs are protected against the effects of the fluids by a bellows. The bellows may be of such a design that it compensates for influences of backpressure.
* Controlled safety valve - Consists of a main valve and a control device. It also includes direct acting safety valves with supplementary loading in which, until the set pressure is reached, an additional force increases the closing force.

The British Standard BS 6759 lists the following types of safety valve:

* Direct loaded - A safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by direct mechanical loading such as a weight, a lever and weight, or a spring.
* Conventional safety valve - A safety valve of the direct loaded type, the set pressure of which will be affected by changes in the superimposed backpressure.
* Assisted safety valve - A direct loaded safety valve which, by means of a powered assistance mechanism, is lifted at a pressure below the unassisted set pressure and will, even in the event of failure of the assistance mechanism, comply with all the relevant requirements for safety valves.
* Pilot operated (indirect loaded) safety valve - The operation is initiated and controlled by the fluid discharged from a pilot valve, which is itself a direct loaded safety valve.
* Balanced bellows safety valve - A valve incorporating a bellows which has an effective area equal to that of the valve seat, to eliminate the effect of backpressure on the set pressure of the valve, and which effectively prevents the discharging fluid entering the bonnet space.
* Balanced bellows safety valve with auxiliary piston - A balanced bellows valve incorporating an auxiliary piston, having an effective area equal to the valve seat, which becomes effective in the event of bellows failure.
* Balanced piston safety valve - A valve incorporating a piston which has an area equal to that of the valve seat, to eliminate the effect of backpressure on the set pressure of the valve.
* Bellows seal safety valve - A valve incorporating a bellows, which prevents discharging fluid from entering the bonnet space.

In addition, the BS 759 standard pertaining to safety fittings for application to boilers, defines full lift, high lift and lift safety valves:

* Lift safety valve (ordinary class) - The valve member lifts automatically a distance of at least 1/24th of the bore of the seating member, with an overpressure not exceeding 10% of the set pressure.
* High lift safety valve - Valve member lifts automatically a distance of at least 1/12th of the bore of the seating member, with an overpressure not exceeding 10% of the set pressure.
* Full lift safety valve - Valve member lifts automatically to give a discharge area between 100% and 80% of the minimum area, at an overpressure not exceeding 5% of the set pressure.

The following table summarises the performance of different types of safety valve set out by the various standards.