Cast Carbon Steel Gate Valve | AA-04
Ref: AA-04
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A. BONNET
Bonnet design is elliptical for 150 lbs class valves, and circular for bigger ratings. In all cases bonnet flange thickness is designed to work under most severe conditions according to ASME B16.34. Body bonnet connection is flat face for 150 lbs class valves, and male-female for bigger ratings. On request other connections such as RTJ or pres-sure seal may be supplied. Auxiliary connection boxes are provided according to ASME B16.34 for instrumentation, drain, or measure purposes. Bonnet machining is carefully checked to ensure wedge travel to be perpendicular to the bore line, so that operating problems are avoided. Stem nut seating must be parallel to bonnet connection. Stuffing box must be extremely smooth machined to provide perfect tightness without applying too much strength on the eye bolts. Life loaded stuffing box may be fitted for special applications using Belleville springs to improve durability and reliability of the packing seal.
B. YOKE
Depending on the size of the valve between the handwheel and the bonnet a yoke is set. The connecting flange of the yoke to the bonnet must be carefully machined to ensure wedge travel to be perpendicular to the bore line, so that operating problems are avoided. A basement is provided on the bonnet to ensure perfect alignment with the stem nut.
C. GATE
Gate valves NPS 2” and bigger are flexible wedge design, NPS smaller than 2” are solid wedge. Sealing surfaces may be overlaid or not depending on the customer’s requirements. Special manufactures such as SPLIT WEDGE, or SOFT SEATED may be produced for special applications. Sealing surfaces are carefully machined so that long life, small torque, and no leakage are achieved.
D. SEAT
For carbon steel valves seat ring is manufactured from forged steel. The sealing surface is sprayed welded with the material required by customer. Renewable threaded seat is used for NPS 10” and smaller valves, welded seat design is used for NPS 12” and bigger. For stainless steel valves usually integral seat is used, overlaid, or not. Other constructions are available under request. Seat surfaces are carefully machined to provide tightness. Special attention must be taken with the seat ring thread to avoid seizing. Special care is taken to provide hardness difference between seat and wedge according to API 600. For this reason seat rings are heat treated.
E. BODY
The valve body is manufactured of cast steel, or forged steel, depending on the customer’s requirements. In any case ANSI B16.34 pressure-temperature ratings, and API 600, or API 602 minimum wall thickness are strictly fulfilled. Gate valves are bidirectional and may be installed in both vertical and horizontal position. Class 150 bodies are designed with elliptical sections. These sections are carefully calculated in order to prevent stress concentrations. Class 300 and bigger bodies have circular sections to make minimum stresses, under severe working conditions. Sealing rings seating is carefully machined and inspected to prevent leakage between seat ring and body. Seating surface must be 1,6 AARH at least. Tapered machining on seat sealing is controlled to ensure perfect sealing and interchange ability with spare parts. Special care is taken to ensure, body end flanges, and bonnet flange to be parallel and perpendicular to prevent operating problems in line and during testing. Flange facing is spiral smooth finish 125-250 AARH standard machining. Other facings are available under request.
Auxiliary connection bosses are provided according to ASME B16.34 for instrumentation, drain, or measure purposes. Flange dimensions fulfil with ASME B16.5, ASME B16.47 and MSS SP 44. Other flange types may be produced under request.
F. STEM
Stem is made of one piece forged steel. The diameter of the stem fulfil with API-600. Wedge connexion is T type, and has been designed to fulfil with API-591 on a strength test. T head is properly designed to allow the wedge adapt to the stem in any assembling position (vertical or horizontal)Back seat sealing face is carefully machined to provide tightness on pressurized pipe line with valve fully opened. For this reason the surface finish of the packing seal must be smooth enough. Machining of ACME threads is smooth enough to obtain a low operating torque.
G. GLAND ASSEMBLY
The gland flange and the gland bushing push the packing rings to make them seal the stuffing box and the stem. Gland bushing is shoulder type to prevent over strength over the packing. Gland flange is designed with enough resistance to work on the most severe conditions. Gland flange and gland bushing are self adjusting to each other to ensure perpendicular pres-sure on the packing.
H. BACK SEAT
All of our valves have back seat design according to API-600. Carbon steel valves are fitted with renewable back seat 13% Cr minimum. For stainless steel valves, the back seat is directly machined on the body. Overlaid surface is possible under request.
I. STEM NUT
Stem nut is made of different materials such as ASTM A439 D2, Ni-Resist, or Aluminium bronze. Depending on the size and class of the valves rolling bearings are fitted on both sides of the stem nut, in order to make minimum operation torque.