Kv coefficient calculation

Calculation itself is carried out with respect to conditions of regulating circuit and   operating medium according to equations mentioned below. Control valve must be designed to be able to regulate maximal flow quantity at given operating conditions. At the same time it is necessary to check whether minimal flow quantity can be even regulated or not.

Condition is the following ratio   

r > Kvs / Kvm

Because of eventual minus tolerance 10% of Kv100 against Kvs and requirement for possible regulation within range of maximal flow (decrement and increase of  flow),  producer recommends  to select Kvs value higher than maximal operating Kv value:

Kvs = 1.1    1.3 Kv

It is necessary to take into account to which extent Qmax involve precautionary additions" that could result in valve oversizing.

Relations of Kv calculation

Above critical flow of vapours and gases

When pressure ratio is above critical (p2  / p1  < 0.54), speed of flow reaches acoustic velocity at the narrowest section. This event can cause higher level of noisiness. Then it is convenient to use a throttling system ensuring low noisiness (multi-step pressure reduction, damping orifice plate at outlet).

Flow characteristic selection in regard of valve stroke

To make right selection of valve flow characteristic, it is suitable to carry out checking of what stroke values will be reached in different o peration states. We recommend to carry out such checking at least for minimal, nominal and maximal flow rates. The principle for flow characteristic selection is to avoid, if possible, 5 10% of the beginning and end of the valve stroke range.

To calculate valve stroke at different operating conditions with different types of  flow characteristics is possible with the advantage of using LDM´s calculation program me VALVES. The program me serves for complete design of valve from Kv calculation to specification of a concrete valve with its actuator.

Valve flow characteristics

Dimensions and units

Principles for plug type selection

V-ported plugs should not to be used in above - critical differential pressures with inlet pressure p >= 0,4 MPa and for regulation of saturated steam. In these cases we recommend to use a perfo- rated  plug.The perforated plug should be also used always when cavitation may occur due to a high differential pressure value or valve ports erosion caused by high speed of process medium flow. If the parabolic  plug is used (because of small Kvs) for above-critical differential pressures, it is necessary to close both plug and seat with a hard metal overlay, i.e. stellited trim.

Packing – Bellows

Bellows packing is suitable for low and high temperatures ranging from -50oC to 550oC. Bellows ensures absolute tightness to environment. Packing is equipped with safety PTFE packing as standard to prevent medium from leaking in case of damage to bellows. Intensive linear forces are not required.

Application of bellows packing

Bellows packing is suitable for applications with very aggressive, toxic or other   dangerous media that require absolute tightness to environment. In such case, it is necessary to check compatibility of used body material as well as the valve inner   parts material with process medium. It is recommended to use bellows with safety packing preventing medium from leaking in case of damage to bellows when there is an extremely dangerous process medium used.

Bellows is also a great solution to use of process medium either with temperature  below zero when ice accretions cause premature damage to packing or with high  temeperatures when bellows ensures medium cooling.

Service life of bellows packing

Values specified in the table above show minimal guaranteed number of cycles with the valve full stroke when the bellows is fully  lenghtened  and  pressed.  In  regulation,  when  the  valve moves only in a portion of the stroke range at the inner centre of the valve, the service life of the bellows is many times longer then depending on concrete operating conditions.

Standard specificoatins   BODY

Attention:

1.Before installed onto pipes, the product shall always be packaged.

2.Speed controller has been adjusted befor shipment,Please don't adjust it.

3.Body Inseat Has been adjusted in a good position when it leaves the factory, not adjustable .

Cv AVLUE,STROKE AND REDUCED PLUG MANUFACTURING RANGE

FLOW CHARACTERISTICS

 ection view

DIMENSIONS