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Valves & seats have evolved over the years into two distinct classes of designs: the Web Seat / Stem Guided Valve Design and the Full Open Seat / Wing Guided Valve Design. The web seat / stem guided valve design is the most popular, representing 90% of all valve and seat usage.
Full open seats / wing guided valves have been available for years, however their performance as a general rule have never been on a par with web seats / stem guided valves. The introduction of valve over valve fluid ends and triplex pumps was an impetus for renewed interest in full open seats / wing guided valves. On valve over valve fluid ends equipped with full open seats, the seat in the suction pot could be removed without removing the discharge seat; which was not possible with web seats. However the poor overall performance of previous full open seats / wing guided valve designs hindered their acceptance in valve over valve fluid ends such that many rigs used full open valve and seats in the discharge pots and stem guided valves and seats in the suction pots. This practice is testimony to the superior performance of web seat / stem guided valve designs, yet acknowledging the maintenance advantage of full open seats in valve over valve fluid ends.
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While many factors determine valve and seat performance, wear life is ultimately determined by bearing area. The web seat / stem guided valve design maximizes bearing area because the valve flange is designed to bear on top of the webs in addition to the seating taper on the inside of the seat. While there are several different web seat / stem guided valve designs by different manufacturers, the TRW Mission web seat / stem guided valve design has evolved into the best performing design in the industry. The performance of this design is due to the maximization of the seat bearing area and the heavy-duty design of the 4-web seat. The success of this design has resulted in the design becoming the de facto standard in the industry, such that the design is now copied by most competitors. Nevertheless the web seat / stem guided valve design is not without its disadvantages. The valve load that bears on the webs results in an uneven stress level on the seat, which results in non-symmetrical loads, applied to the fluid end as illustrated in Drawing #1. For comparison the loads applied to the fluid end by a full open seats are also illustrated in the accompanying full open seat drawing. The non-symmetrical loads applied to the fluid end by a web seat can over time force the fluid end seat taper out of round which will result in a wash out of the seat taper on the fluid end. This problem is the major cause of washed out fluid ends, rather than poor maintenance by the rig personnel. All web seats have this problem regardless of the number of webs; the problem is particularly acute on National pump fluid ends because of the relief at the bottom of the taper, above the shoulder, in the fluid end.
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The National Supply full open seat / wing guided valve design established a loyal following with a minority of customers who were willing to sacrifice poor performance for the maintenance advantages of full open seats. However in the drilling pump market, this design failed to displace web seats / stem guided valves because of its relatively poor performance due to the limited bearing area.
The development of the inertia welded unibody valve design in 1983 by Roughneck and Novatech was a major milestone in valve design in that the design overcame a major obstacle in the design of valves for full open seats. The design was able to utilize streamlined guide legs that reduced turbulence and valve guide area and thus permitted increasing the available bearing area, which was necessary for improved performance. This design evolved through several design variations including the Harrisburg, PEP and finally the Novatech version.
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The following is a brief discussion of the evolution in design of valves & seats in recent years. The accompanying drawings illustrate the relative and pertinent design details between the different designs. For instance, the drawings include top views of the seats and pie charts that illustrate the relationship of flow area, metal-to-metal bearing area, insert bearing area, and valve guide area, and unused area for all the different designs. API specifications dictate the total area in a specific size that is available to the designer to be utilized among the individual areas; for example flow area cannot be increased without sacrificing the area available for metal-to-metal bearing area or other areas. However flow area may be reduced and other areas increased proportionally if turbulence can be reduced through a more streamlined valve guide design. All the drawings are drawn to scale so that the reader can make a direct comparison of the different areas among the different designs.
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Drawing #1: TRW Mission web seat / stem guided valve design; a proven design that maximizes metal-to-metal seat bearing area to reduce metal wear. The major disadvantage of the seat is the non-symmetrical fluid end load that causes out of round seat tapers in fluid end, washed out decks, and / or cracked fluid ends.
Drawing #2: National Supply full open seat / wing guided valve design; an old but proven design, however the design is performance limited by the large legs that require a large seat opening to maintain adequate flow area, thus metal-to-metal seat bearing area is sacrificed, resulting in accelerated metal wear. Also large, wide legs cause fluid turbulence behind the legs, resulting in damage, due to the turbulent flow, to the valve insert and wash failures between the valve and seat. As with all full open seats, the symmetrical load to the fluid end does prevent out of round seat tapers and washed out fluid ends; also suction seats can be removed without disturbing the discharge seat on valve over valve fluid ends.
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Drawing #3: Harrisburg Roughneck full open seat / wing guided valve design. In 1983 Novatech and Roughneck pioneered the inertia welded unibody valve design for well service valves. This design combined the impact resistance of a forged valve body with the precision detail of investment cast guide legs. This design allowed for thinner, streamlined guide legs and a large open area above the valve legs and below the valve body that eliminated the turbulence associated with old designs in which the guide legs were forged into the main valve body. The thinner guide legs also allowed for the reduction in the seat opening without sacrificing flow area; metal-to-metal seat bearing area could then be increased. Harrisburg bought the Roughneck product line in 1985 and introduced the Roughneck Mud Pump valve & seat in 1987. The weakness in this design is the excessive insert bearing area at the expense of metal-to-metal bearing area that results in accelerated metal wear. Contrary to popular opinion the insert does not cushion the valve; rather the sole purpose of the insert is to seal around solids in the mud. A further weakness of this design and all snap-on valve insert designs is the tendency for the valve to fail by washing around the backside of the insert. Also snap-on inserts never properly fit the insert groove and tend to be out-of-round after installation. This out-of-roundness often results in premature insert seal failure and washing between the valve & seat. Also stretching the snap-on insert during installation results in retained residual stress in the insert that shortens insert life.
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Drawing #4: Mission Service Master II full open seat / wing guided valve design. Essentially a well service valve with a top stem added. The design sacrifices metal-to-metal bearing area for excess flow area. Also the small insert lacks sufficient section thickness and strength which results in premature insert failures.
Drawing #5: PEP full open seat / wing guided valve design. Actually developed and manufactured by Novatech for PEP; Novatech currently manufactures this valve & seat as part of its product line. The valve is a major improvement over the Harrisburg Roughneck valve; accomplished by increasing metal-to-metal bearing area in favor of reduced insert bearing area. Serrations are added to the bottom of the insert groove to prevent this common type of seal failure. A weakness of this design and all snap-on valve insert designs is that snap-on inserts never properly fit the insert groove and tend to be slightly out-of-round after installation. This out-of-roundness often results in premature insert seal failure and washing between the valve & seat.
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Drawing #6: Novatech Full Open Seat / Wing Guided Valve design. The latest evolution of full open seat & wing guided seat design features a large metal-to-metal bearing area for long life and the new “Cast In Place” insert design. The “Cast In Place” insert results in a perfectly round inset that prevents premature seal failures of the inserts. Serrations on the bottom and top of the insert groove lock the insert in place and prevent washing around the back of the insert. As the insert is molded around the serrations, inserts failure due to tears from the serrations are eliminated. Most importantly the insert is not stretched over the valve during installation; there are no residual stresses from installation to shorten insert life. In actual performance valve and insert life are markedly improved over all previous valve & seat designs.
Drawing #7: Novatech Stem Guided Valve / Web Seat. A new valve design that is interchangeable with the Mission Web Seat Design. The unique welded, hollow design results in a valve that can be inexpensively manufactured, competitive with foreign imports. The “Cast In Place” insert improves performance over the original Mission Design Stem Guided Valve.
Drawing #8:Novatech puller head for full open valve seats. In the past a major nuance with full open seats was seat removal from the pump. Old style “split jaw” puller heads were prone to breakage. The bar style puller heads were difficult to use in valve over valve fluid ends. The drawing illustrates the use of the Novatech Puller Head in valve over valve fluid ends. This puller head has been redesigned and strengthened so that now the puller stem fails before the puller head.
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High Temperature Inserts: Novatech offers a special insert for high temperature drilling applications. High Temperature Inserts tend to be stiff and rigid, as such, these inserts require near perfectly round seats to seal effectively. Web seats tend to be significantly more out-of-round that full open seats because when heat treated the webs result in different shrinkage rates when the seats are quenched. Whereas the full open seats, with a uniform cross section, tend to remain near round when quenched. Also valve inserts, either snap-on or plate retained, tend to be forced out-of-round during insert installation. The Novatech cast-in-place inserts are very close to perfectly round and free of any residual stress. To achieve this near perfect roundness that the rigid High Temperature Inserts require, Novatech only offers high temperature inserts in the full open valve with the cast-in-place insert configuration. The roundness of Novatech valves and seats will alone solve some high temperature problems; the Novatech full open valve and seat with high temperature inserts are the preferred valve and seat for severe high temperature applications.
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Summary: The Novatech Full Open Seat / Wing Guided Valve with the cast-in-place insert is the pinnacle of valve and seat design. The performance of these valves and seats exceeds the performance of the popular 4-web seat / stem guided valve design. The Novatech full open seat / wing guided valve achieves superior performance with the full open seat design that allows changing suction valve seats without disturbing the discharge seat on valve over valve triplex fluid ends. The Novatech seat puller is exceptionally simple, strong, inexpensive, and easy to use. Often ignored or forgotten is the advantage of a uniform fluid end load provided by full open seats, which reduces premature fluid end failures due to washed out seats and/or cracked fluid ends. This advantage alone almost mandates full open seats in lieu of 4-web seat designs. For customers who are strongly attached to 4-web seats, the Novatech Stem Guided Valve / Web Seat provides an economical alternate with superior performance due to the cast-in-place insert feature.
Novatech Corporation is an oilfield manufacturing company located in Dallas, Texas. Since 1981, Novatech has manufactured valves and seats for several different manufacturers, which were marketed under the Harrisburg, Mission, National, Roughneck, Oteco, and PEP brand labels. The Novatech plant is the oldest continous operating valve and seat manufacturing facility in the U.S. In 1994 Novatech began marketing valves and seats under the Novatech brand label. Starr Pitzer Jr. is the President of the company.
George Blume, a Product Development Consultant with Novatech, authored this paper. George is an engineering graduate from the University of Texas in Austin and has worked in valve and seat design since 1975. George designed the original Roughneck valve and the subsequent Harrisburg, PEP, and Novatech designs.
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