Seated type (Glob) valves; By placing or lifting the flap attached to the end of a shaft on the fluid passage hole, they perform their duties by cutting and opening the fluid passage.
The flaps are normally in the form of a plate.
The control valves have parabolic projections at the ends of the flaps extending into the passage hole.
Globe valves have different flow characteristics depending on the valve type.
Clean, neutral or aggressive liquid, gaseous fluids
It indicated. Otherwise, the flow is not correct.
Hot and Cold Water Installations, Steam Installations, Hot Oil Installations, Petrochemical Plants, Machinery Manufacturing, Special Vehicle Manufacturing, etc.
Manually, with motor actuators, with magnetization in short strokes (Solenoid valves)
It can be from DN 15 to DN 400.
Up to PN 300 can be reached. However, they are generally manufactured up to PN 40.
In valves, pressure difference between inlet and outlet pressures (DIN 3356) is given below the nominal pressure in some pressure and nominal dimensions. (For example: PN 16, DN 200 Globe Valve Pressure difference can be maximum 14 bars.)
This means that if one end of the valve is open to the atmosphere, the operating pressure of the valve may be 14 bar, not the nominal pressure.
If we calculate the force faced by the valve valve against the fluid pressure when it is in the closed position or is about to close;
Force (kgf) = Diverter effective area (cm2) x Pressure (bar),
When calculating for a DN 200 valve, if Pressure = P = 14 bar (Through hole diameter = D ≈ 200 mm = 20 cm);
The force exerted by the pressure of the fluid against the clapper rises as = F = [(3.14 x 202) / 4] x 14 = 4 .396 kgf. When we want to close the valve, this force must be applied against the fluid over the shaft by the operator or actuator. . When fluid pressure increases, this force can create serious problems.
In order to reduce this force to reasonable levels, pressure balancing is carried out by transferring fluid pressure to the back surface of the flap by various methods.
There are pressure balance bellows and pilot valve valves. In cases where this is not applicable, balancing can be done with shorter lines using smaller valves. Such applications are generally used in valves of nominal size DN 65 and above. Since we know that the force increases with the square of the pressure,
DN 50 valve for 16 bar pressure; F = [(3.14 x 52) / 4] x 16 = 314 kgf and remains in a size that can be met by the operator with a ball screw system.
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It can expand from -2000C to + 4000C. However, they are generally manufactured for the range of –500C and + 2500C.
Copper alloys (Brass, Bronze), Cast iron, ductile iron, steel and stainless steel Casting, and Stainless Steel, PVC, PP
Screwed, Flanged, Welding Mouth
DIN 3356, TS 15, ANSI B16.34, BS 1873, BS 5352, BS 5152, BS 5154, BS 5160
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They provide precise flow control.
A good sealing is ensured by the flap’s contact with the seat, without friction, by sitting.
There are types suitable for high pressures and temperatures.
They are also suitable for gaseous fluids.
They are suitable for opening and closing very often and many times.
Compared to the gate valves, this force application positively affects the sealing as the shaft presses the valve directly on the seat. Therefore, Globe valves are preferred as a shut-off valve instead of a slide valve, especially in cases where high pressure flow can create an atmosphere-hazardous atmosphere.
Pressure losses are high due to their structure.
They contain dead volume. Residues may accumulate inside the valve.
Flow is possible only in the direction indicated on the valve. It is not suitable for two-way operation.
In large nominal dimensions, enormous forces act on the opening and closing spindle. This force makes it difficult to close. When it comes to controlling large flows; It is a common practice to separate the flow into two or more smaller lines and use small Globe valves.
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Spindle screw out and rising flywheel
Spindle screw outside and non-rising flywheel
Shaft screw inside and rising flywheel
Shaft screw inside and non-rising flywheel
Of the mentioned types
Advantages:
For those with outside screw; the screw is not in contact with the fluid, ease of maintenance, ease of use for fluids with aggressive and corrosive properties,
In rising national and flywheel; visual stroke control,
In non-rotating nations; long seal life.
In non-rising flywheels; ease of actuator application.
Disadvantages
In rising flywheels; needing more space for flywheel,
Although the spindle screw has all the advantages of non-rising flywheel and non-rotating spindle type, manufacturing costs are high.
Also; If the flywheel is not removed from the valve body with a bridged cap system, it is difficult for the operator to open and close the valve due to the overheating of the flywheel in case of working with hot fluid.
Straight Through: Generally, there are high pressure losses. Although its name is straight-through, this only applies to connection to the installation. It draws a fluid “S” in the valve.
Corner: They provide advantages for plumbing corner points.
Y- type: Pressure losses are reduced by about half. KV value increased. There is less risk of fluid residue in the valve. However, the stroke is longer.
Elastomer braid or package packing:
It is a classic seal type. During operation, in case of continuous monitoring and leakage, it must be compressed and continue to provide sealing.
Asbestos is carcinogenic, nowadays mesh seals made of non-asbestos material are used. The most common of these are made of pure graphite material.
Self-sealing O-Ring packing:
O-Ring packing groups made of elastomer material selected for temperature and pressure stages, with long-term maintenance and follow-up, without requiring maintenance, follow-up and re-compression, with proper and clean production of seal housing and shaft surfaces.
However, the inability of the elastomer material to withstand temperatures above 150 ° C generally limits their range of use to the temperature constraint.
Metal Bellows seal:
Metal bellows seals are used for “0” sealing to the environment since Elastomer seals need to dry and re-tighten in the installations around the shafts where sealing is important to the environment. Such seals safely provide seal sealing throughout the mechanical life of the metal bellows, without the need for follow-up. They reduce maintenance costs.
It is possible to manufacture “Pressure balanced” valves with this seal type.
Linear (linear) characteristic
Each unit increase in stroke provides an equal increase in flow rate.
Quick opening characteristic
This characteristic is suitable for situations where the maximum flow should be reached immediately when the valve starts to open.
Equal proportional characteristic
Among these three characteristic types, it is the most used in control valves. In this type, the flow change in each unit stroke stroke of the valve is directly proportional to the flow obtained before the movement.
At the beginning of opening in these valves, the flow rate is low when the stroke is small, and when the valve approaches the fully open position, the rate of flow change is high when the stroke is completed.
This characteristic allows for a good and precise adjustment, from less strokes where the control is more difficult, to a half open position in the small flow area
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In cases where leakage can be dangerous, if we need to use globe valves; we can install the two valves one at a time in series. If there is a leak in the inlet, a spare valve will be available in the system. With this system, we distribute the pressure drop to two valves and reduce the total noise level.
Reason Behind use of Glob Valve
Since the sealing is provided by sitting on one of the flap and seat surfaces, if the fluid is not clean, sealing will not start and leakage will begin with the introduction of solid particles between the two surfaces. The cleanliness of the fluid is very important in these valves as well as in every valve.
If the fluid used may be freezing or solidifying when the temperature drops, the body should be heated in a pattern such as a serpentine and jacket.
In terms of overall energy saving; It should not be forgotten that the valves have large surfaces that will cause heat loss to the environment, and the valves where different fluid passes from the ambient temperature must be isolated.
Due to their nature, such valves can remain in a semi-open position without causing any problems. However, it is not correct to hold it for a long time in positions that are very close to closing, that is, the valve is kept too tight. In these cases where the valve’s rated size is greater than it should be, the fluid velocity increases significantly in the small gap left between the valve and the seat. The rapid passage of the fluid leaves traces that begin as capillaries on the seat and valve surface. These scars grow over time and the valve begins to miss. This fast flow also means high noise. In valves to be used for adjustment, valves with a “flow factor” appropriate to the design flow should be selected. Large capacity valve selection reduces adjustment capability. In some cases, one or two taps of nominal diameter valves may be used from the pipe nominal diameter.
The most common problems in such valves are again; sealing surfaces are wear and seal leaks.
In case of leakage from shaft packing, the packing should be compressed to prevent leaks. But If the valves have been in the warehouse for a long time before they are connected to the installation or have reached the limit of compressibility, the seals may lose their elasticity and become unable to prevent leakage. In this case, repair is not possible and the packing must be replaced.
In metal bellows seal valves developed to completely prevent packing leaks, maintenance repairers do not need to be followed to tighten the packing. In these valves, if the metal bellows completes its mechanical life (according to the manufacturer’s life values such as 5.000, 10,000, etc. full opening) and is drilled, it must be replaced with the new stuffing box.
When repair work is required as a result of damaged sealing surfaces, processes such as grinding and lapping of surfaces are obligatory. Therefore, it would be more correct to have this kind of repair work done at the manufacturing company.
As a result of problems such as cavitation, erosion, if there is wear and perforation in the body, if there is a technical infrastructure, it can be repaired by taking necessary precautions and fulfilling the technological requirements, especially by welding fillers in steel valves.
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