Until the development of the Novatech Cast-N-Place™ insert valve, stem guided valves for web seats had proven themselves to provide the best performance for mud pump service; this performance level was achieved because this design maximized metal-to-metal bearing area, as shown in the drawing to the right. However, this design is not without problems. The valve impact loads are applied to the seat webs, as well as the seating bevel on the inside of the seat; unfortunately, valve loads applied to the seat webs are not uniformly distributed to fluid end deck taper.
The distribution of these loads has been studied with a Finite Element Analysis (FEA) computer program; the results are illustrated to the left. The FEA program divides the part into hundreds of small Hexahedrals or cubic elements, the program then is able to calculate the loads and stresses on each element individually.
The results are then added together to calculate the results on the entire part. With these programs, loads and stresses can be calculated on very complex parts, such as web valve seats. In the illustration, red areas delineate large transmitted loads, in this case loads transmitted to the fluid end deck taper. Blue areas delineate low transmitted loads. Note that the areas of high loads are always inline with the webs. After hundreds of thousands of cycles of the valve impacting the seat and the seat transmitting these impact loads to the fluid end deck, the fluid end deck is eventually forced out-of-round from these non-uniform loads.
One can observe the evidence of this phenomenon by examining used seats pulled from a pump,
as shown in the photo on the right. The shiny areas on the seat taper indicate where the taper was in good contact with the fluid end deck taper; the dark areas are where there was little or no contact. When the shiny area on a seat taper becomes very narrow, the seat is in imminent danger of washing out. The crack in the hole at the center of the seat on the right is due to the seat breathing in the deck because of insufficient contact with the taper. The next picture, on the left, shows the same seat from a different angle; the seat has washed out because of the lack of a seal due to insufficient contact with the out-of-round deck. Full open seats are just the opposite of web seats in their relationship with the fluid end.
The Novatech design on the right maximizes metal-to-metal bearing area by utilizing inertia welded uni-body valve construction; the valve impact loads are uniformly transmitted to the fluid end. When these loads are analyzed by FEA, as shown by the FEA image to the immediate left, it can be seen that seat loads are uniformly distributed around the circumference of the seat. This uniform loading eliminates peak loading as seen on web seats and reduces the unit loads at any specific point on the seat taper. Because of the uniform loading of full open seats, a consistently even contact area is maintained with the fluid end deck taper, as shown by the drawing at the lower right. It is true, that when web seats are installed in new fluid ends or recently lapped fluid ends, that they also exhibit a uniform contact area w
ith the fluid end. However, after the use of some number of web seats, the contact area begins to change, as shown by the photos above. To the contrary, when full open seats are installed, the contact area remains uniformly consistent, as shown on the left. Full open seats eliminate premature washouts and can thus be characterized as fluid end saviors!