Back pressure valve

A back pressure valve includes a tubular body having pin and box connections at its outer ends and formed of two tubes connected by double step straight threaded connectors with a seat ring captured between the two tubes. A ball is urged against the seat ring by a helical compression spring. A triple slotted tubular spring support is screwed into the outlet portion of the body. A hex headed cylindrical post at the upper closed end of spring support fits snugly but slidably with the spring and centers the spring. The dimensions of the spring and spring support are such as to prevent the spring from buckling. The flow path through the slots and around the support is as large as that through the seat ring, which is about equal to that through the pin connectors of the body tubes, whereby the wall thickness of the pin connectors is large. The support can be removed with a socket wrench. A release tool can depress the ball off its seat to release fluid pressure.

SUMMARY OF INVENTION 
(a) Field of Use 
This invention pertains to valves and more particularly to spring loaded 
ball check valves adapted for use in oil-field tubulars to prevent back 
flow of drilling, formation, or other fluid. 
For example, in a drill string used for work over of an existing petroleum 
well a check valve is placed close to the drill bit to prevent back flow 
of drilling fluid when high pressure is encountered at the bottom of the 
well. A typical work over drill string, to be run inside existing 
production tubing, may include, in order from the bottom up, a drill bit, 
a thirty foot length of tubing, two back pressure valves, e.g. valves 
according to the invention, in series, a landing nipple (short length of 
pipe with a seat adapted to engage a ball dropped down the tubing, and up 
to several thousand feet of tubing. 
Another example of a use of such check valves, including valves embodying 
the invention, is as a safety valve at the top length of drill pipe, added 
quickly to the drill string if high pressure is encountered. Later if it 
is desired to release the pressure, a release tool is employed, which is 
screwed into the top of the valve body to push the ball off its seat. 
The invention further relates to a release tool for opening the valve to 
release pressure. 
(b) Point of Departure 
Heretofore a known back pressure valve, somewhat as shown in FIG. 1 of the 
accompanying drawings, included a three piece tubular body 21, 23, 25 with 
threaded pin and box connections on the ends of each piece whereby the 
pieces were screwed together and adapted to be connected to the adjacent 
drill string members. Between the upper piece 21 and middle piece 23 was a 
replaceable seat ring 25, captured between annular shoulder 27 on middle 
piece 23 and pin 29 at the lower end of upper piece 21, an O-ring 31 
sealing between pin 29 and ring 25. 
A cross shaped center support 33 was disposed at the juncture of middle 
piece 23 and lower piece 25 of the tubular body. Support 33 included a 
downwardly extending leg 35 received in lower piece 25 and two outwardly 
extending arms 37, 39 resting on top of threaded pin 41 at the top of 
lower piece 25. An upwardly extending post 43 completed the center 
support. 
A compression helical spring 45 centered about post 43 at its lower end 
urged a ball 47 against seat 25. The diameter d of the flow passage 
through the seat ring 25 was smaller than the diameter D of the flow 
passage through the upper and lower pieces of the body. 
Objects of the Invention Include 
1. Increased body strength. 
2. Prevention of flow blockage by spring support moving up in the middle 
piece (spring chamber) of tubular body. 
3. Prevention of flow blockage arising by buckling of the spring. 
4. Prevention of buckling of spring. 
5. Elimination of choke effect of seat ring. 
Brief Description of Invention 
According to the invention a back pressure valve suitable for 5000 up to 
20,000 psi working pressure comprises a two piece body including an upper 
or inlet tube and a lower or outlet tube screwed together with a two step 
straight threaded pin and box connection and provided with theaded pin and 
box connectors at the body ends for making connection with other drill 
string members. A seat ring having the same inner diameter as the inlet 
tube and the minimum inner diameter of the outlet tube is captured between 
a shoulder on the outlet tube and the pin at the lower end of the inlet 
tube. A spring support is screwed into the lower end of the outlet tube. 
The spring support includes a tubular lower portion having three slots in 
is sides leaving three legs supporting a disc at the upper end of the 
tube. The tube outer diameter is smaller than the inner diameter of the 
outlet tube leaving a flow passage therebetween having a cross sectional 
area at least as large as that through the seat ring. A hexagonal tipped 
center post rises from the upper side of the disc atop the support tube. A 
short helical compression spring centered about the center post urges a 
ball against the seat ring. The post extends half the distance between the 
lower end of the ball and the lower end of the post. When the ball moves 
down to the limit imposed by the top of the post, the spring is fully 
compressed about the post. 
Advantages of the Invention 
Advantages of the invention include: 
(1) The equalization of the seat ring inner diameter and the inner 
diameters of the connector pins provides greater wall thickness for the 
pins and hence greater strength. 
(2) The two step straight threaded connection between the two body parts 
gives greater strength. 
(3) The two part body is simpler and stronger than a three part body. 
(4) The fluid path through the body is wholly outside of the spring so 
buckling of the spring will not block fluid flow. 
(5) The spring support is anchored to the body so it will not pop up and 
block fluid flow. 
(6) The spring is so short it does not buckle. The unsupported length, i.e. 
the part between the top of the center post and the lower end of the ball 
is less than twice the outer diameter of the spring. The full compressed 
length of the part of the spring between the lower part of the ball and 
the top of the support disc is about the same as the length of the center 
post. (Note that the upper part of the spring serves as a cup to receive 
the ball and does not partake fully in the spring compression.) 
(7) The flow path through the seat ring is as great as the minimum flow 
paths through the body tubes. 
(8) There is no choking of the flow path past the spring support. 
(9) The three slots in the support tube is a number that reduces turbulence 
and hence reduces wear which a swirling abrasive might cause. 
(10) The spring support is easily released with a socket wrench engaged 
with the hex or other non-circular tip on the center post.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to FIG. 2, there is shown a valve comprising tubular body 101 
including upper or inlet tube 103 and lower or outlet tube 105. There is 
an internally threaded box 107 connector at the upper end of inlet tube 
103 and an externally threaded pin connector 109 at the lower end of 
outlet tube 105. Preferably connectos 107,109 are correlative and of the 
high pressure Hydril type employing straight threads on two different 
diameters forming a two step thread on each connector, but whatever 
connector is required for incorporation in the desired drill string can be 
provided. 
The upper and lower tubes are screwed together, tube 103 being provided at 
its lower end with an externally threaded pin connector 111 which screws 
into an interally threaded box connector 113 at the upper end of tube 105. 
Connectors 111 and 113 are preferably of the high pressure, Hydril, 
straight threaded, two step type. 
Lower tube 105 includes an upwardly facing internal shoulder 115 against 
which bears a hard steel seat ring 117, held against the shoulder by pin 
111. An O-ring seal 119, made of rubber or other oil and water resistant 
elastomeric material, is compressed between ring 117, lower tube 113, and 
pin 111. 
A valve closure comprises a ball 121 which seats and seals against seat 
ring 117 and is urged against the ring by the upper end of helical 
compression spring 123. The spring bears at its lower end against tubular 
spring support 125 which is closed at its upper end by disc 127. A center 
pin or post 129 extends upwardly from disc 127 nearly half way into the 
spring. Spring support 125 is threaded at its lower end with straight 
threads 131 and is screwed into threaded socket 133 against annular 
shoulder 135. 
There are three slots 137 in tube 125, equiazimuthally spaced apart, as 
best shown in FIG. 2A, leaving three legs or struts 139 therebetween. The 
three slots provide fluid passage through the support. Three slots are 
preferred to some other number of slots such as one, two, four or five, 
because this number, three, is believed to produce the least turbulence. 
Note that the wire diameter w of the helical spring is about the same or 
only slightly smaller than the coil spacing c, the distance between 
adjacent turns of the spring. Also note that the length of the center post 
129 equals 3 turns I, II, III and that there are three turns IV, V, VI 
from the top of post to the bottom of ball 121 and that top turn VII forms 
a cup to receive the ball. Note that the coil inner diameter of the spring 
is only slightly larger than the outer diameter of hexagonal post 129, the 
spring making a snug sliding fit with the post. Also note that the 
distance from the bottom of the ball to the top of the post, is about the 
same as the length of the post. These dimensions avoid buckling of the 
spring. 
When it is desired to replace the spring support, a socket wrench, such as 
wrench 141 shown in FIG. 5, may be employed. The hexagonal socket 143 is 
adapted to engage hexagonal head 145 on the upper end of post 129. By 
turning handle 147, the support can easily be unscrewed from socket 133. 
If the valve is used as safety valve, i.e. a temporary closure at the upper 
end of a string of tubing, the pressure locked in the tubing can be 
released by inserting a release tool 149 (see FIGS. 3 and 4) into the 
tubing and screwing its externally threaded portion 151 into the box at 
the upper end of the tubing. A stinger rod 153 extends through the length 
of the tubing into the top of upper tube 103 of the valve and presses down 
on ball 121 to open the valve. A plurality of paraxial holes 155 in rod 
153 allow fluid flow out through the tool to relieve the pressure. 
While a preferred embodiment of the invention has been shown and described, 
modifications thereof can be made by one skilled in the art without 
departing from the spirit of the invention.