Plunger Pump Lubrication System and Method

Abstract

A system and method for lubricating a packing gland of a positive displacement plunger pump. The system includes a pressure regulated lubricant discharge from the packing gland. The pressure regulated lubricant discharge maintains a positive pressure in the packing gland to resist unloading of the packing.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No. 61/321,335 filed on Apr. 6, 2010.

BACKGROUND

This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

This invention relates generally to plunger pumps, and more particularly to a lubrication system and method. The use of packing (i.e., packing gland) in pumps and other apparatus having reciprocating, slidable or rotatable members for moving fluids or mixed fluids and semi-solids is well known. The packings are typically made up of a resilient or at least compressible material which serves a sealing purpose through its compression and retention of a lubricant, most often an oil or graphite. The degree of compression in adjustable type packing glands can be made by tightening a member of the packing gland. Non-adjustable, fixed length, packing glands which are commonly used as well service pumps do not facilitate altering the compression by tightening a member. In plunger pumps utilizing non-adjustable packing glands, pressurized lubricant is provided to the packing gland to compress the packing in the stuffing box. It is a desire to provide a lubricating system and method for fixed length packing glands for positive displacement plunger pumps.

SUMMARY

A positive displacement plunger pump according to one or more aspects of the invention comprises a plunger reciprocally disposed through a packing gland, the packing gland comprising an inlet and an outlet; a pressurized lubricant fluidicly connected to the packing gland at the inlet; a pressure regulated discharge device fluidicly connected to the packing gland at the outlet.

A method according to one or more aspects of the invention comprises injecting a lubricant under pressure into a packing gland through which a plunger is reciprocating, and discharging the lubricant from the packing gland in response to an outlet pressure greater than a selected relief pressure. According to one or more aspects of the invention, the lubricant is injected as a pressure to load the packing gland. The selected relief pressure may be less than the injection pressure and high enough to maintain a positive pressure in the packing gland to resist unloading of the packing gland.

The foregoing has outlined some of the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a cut-away view schematically illustrating a plunger pump according to one or more aspects of the invention.

FIG. 2 is an expanded view of the packing gland and plunger illustrated in FIG. 1.

FIG. 3 is an expanded view of a portion of the packing gland illustrated in FIG. 2.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact.

FIG. 1 is a cut-away view schematically illustrating a plunger pump, generally denoted by the numeral 10, according to one or more aspects of the invention. Depicted plunger pump 10, for example a well service pump, includes a fluid end 12 (i.e., output manifold), power end 14, and a plunger 16. Fluid end 12 comprises a suction valve 18 and a discharge valve 20 in fluid communication through first bore 22. A cylinder 24 (i.e., cross-bore) intersects first bore 22 and has a port 26. A stuffing box 28 (e.g., packing nut) comprising a packing gland 30 is disposed at port 26. In the depicted embodiment, packing gland 30 is described as a fixed length or non-adjustable packing gland. Plunger 16 reciprocates through stuffing box 28 and packing gland 30.

Depicted plunger pump 10 comprises a lubrication system, generally denoted by the numeral 32, fluidicly connected to packing gland 30. FIG. 1 schematically illustrates lubrication system 32 comprising a lubricant 34 (e.g., oil, grease) connected through an inlet port 36 to packing gland 30. In the depicted embodiment, lubricant 34 is provided under pressure, represented by pump 38, through a one-way valve 40 to packing gland 30. Lubrication system 32 further includes a pressure regulated discharge line 42 connected to packing gland 30 through a discharge port 44. Discharge line 42 comprises a pressure regulating device 46 (e.g., orifice, relief valve) and discharge containment vessel 48. Vessel 48 may comprise a tank, pan, line or other vessel for containing the lubricant in an environmentally acceptable manner. Pressure regulating device 46 includes an adjustable pressure back or relief pressure. For example, the relief pressure can be set at a pressure less than that of the pressurized lubricant at inlet 36 so that lubricant can be discharged from packing gland 30 through discharge line 42. The relief pressure can also be set at a level sufficient to maintain a desired sealing compression of packing set 52 and less than the pressure at which lubricant 34 is expelled past wiper plug 54.

Aspects of lubrication method and system 32 are now described with reference to FIGS. 1 to 3. Pressurized lubricant is plumbed into stuffing box 28 (e.g., packing nut) at inlet port 36 and through a conduit 19 formed through lantern ring 50 that is disposed between a packing set 52 (i.e., high pressure seal) and a wiper seal 54 (i.e., low pressure seal). Wiper seal 54 functions as the barrier on the low pressure side of stuffing box 28 which is only subject to lubrication pressure. The left side, facing power end 14 (FIG. 1) is the low pressure side in the depicted embodiment. Wiper seal 54 is depicted oriented in a direction for use with a liquid (i.e., oil) lubricant. According to one or more aspects of the invention, wiper seal 54 does not need to be oriented in different directions for use with different lubricants (e.g., oil and grease) as may be needed with traditional packing glands.

In the depicted embodiment, packing set 52 comprises seal rings 56 and a header ring 58. An adapter ring 60 provides a sealing interface between fluid end 12 and stuffing box 28. Some packing glands utilize a single height and double height vee rings. Three single height vee rings are depicted in FIGS. 2 and 3. Lantern ring 50 functions as an anti-extrusion element for the adjacent seal ring 56, it has a slightly loose fit with the OD of plunger 16 and the ID of stuffing box 28. Seal rings 56 have an interference fit with the OD of plunger 16 and the ID of stuffing box 28 to provide the high pressure seal, each cupped element will act as an anti-extrusion element for the ring closest to the pump pressure. Fluid pressure linearly decays across the seal rings from the high pressure side (i.e., the fluid end side) to atmosphere side with the seal ring closest to atmosphere biting hardest on plunger 16. Header ring 58 has an interference fit with plunger 16 and stuffing box 28 and acts as an energizing ring to produce initial compression on the installed packing set 52. Since packing gland 30 is designed to be non-adjustable, a biasing force is required to produce the required initial compression on the seal rings, this biasing force is provided by header ring 58. Header ring 58 further serves as a low pressure seal which introduces sufficient force on seal rings 56 as pressure increases to allow rings 56 to gain a bite on plunger 16. Adapter ring 60 functions to complete packing gland 30 height and houses seals to hermetically seal the connection of stuffing box 28 and fluid end 12. The depicted packing gland 30 is illustrative of a configuration for a well service pump.

Packing set 52 is arranged designed to have small voids 62 (FIG. 3) formed between the adjacent rings 56, 58. Voids 62 allow for a small volume of lubricant to exist which aids in sealing and lubrication during the stroking of plunger 16. Due to the geometry of packing set 52, injection of lubricant 34 will fill any voids within stuffing box 28. If lubricant 34 (e.g., oil or grease) injection occurs on the suction stroke of plunger 16, the lubricant 34, which is at a higher pressure than the suction pressure of fluid end 12, will force packing set 52 to momentarily separate from contact with plunger 16 and stuffing box 28 and allow lubricant 34 to enter packing gland 30. It should be noted that the injection of lubricant 34 occurs randomly with respect to the pumping cycle. This filling cycle essentially fills most voids 62 in packing set 52 with incompressible lubricant 34. When plunger 16 starts the compression stroke, the fluid forces acting on packing set 52 increase and begin to force lubricant 34 out of voids 62. In other words, seal rings 56 and header ring 58, which have high shear strength, will become fluid at high pumping pressures and extrude into voids 62 displacing the lubricant which has minimal shear strength. Since wiper seal 54 is capable of holding a high lubricant pressure, for example 1,000 psi or more, lubricant 34 will primarily force its way through packing 52 toward the pumpage, i.e., fluid end, as illustrated by the arrows in FIG. 3.

According to aspects of the prior art plunger pumps, extruding lubricant 34 from the voids has the effect of unloading packing seal rings 56 and header ring 58 as it lifts them from contact with the OD of plunger 16 and the ID of stuffing box 28 resulting in the ring 56 closest to atmosphere assuming more of the sealing duty and biting very hard on the plunger, which results in wear and fatigue failure. Essentially every stroke is a battle between the pumpage and lubricant to see which will overcome the other. On compression strokes where the incoming lubricant was not enough to fill all the voids the unloading effect will be minimized or not occur at all. This battle continues until the packing fails or the wiper seal is destroyed due to the excessive pressure that bypasses the packing seal rings. Another drawback of the contemporary plunger pumps is that at times the wiper seal is actually blown out by exposure to high pressure that escapes the seal rings 56, 58. This is a direct effect of the escaping lubricant unloading the packing seal rings and allowing pumpage to enter the low pressure region.

Lubrication system 32 comprises a pressure regulating device 46, such as without limitation a fixed orifice plate or an adjustable in-line relief valve to maintain positive pressure in packing gland 30 and to allow damaging high pressure to safely discharge to a containment vessel 48. The relief pressure of pressure regulating device 46 may be adjusted for variance in lubrication systems, pumping conditions, and condition of packing and parts. It is possible for all available voids 62 in stuffing box 28 to be filled with an incompressible lubricant 34 just prior to the start of a power stroke. In contrast to contemporary plunger pump and lubrication systems, as plunger 16 begins the power stroke and pressure forces build up, lubricant 34 that is displaced from voids 62 pass through packing set 52 as shown by the arrows in FIG. 3 to discharge port 44 (FIGS. 1, 2) and through discharge line 42 to containment vessel 48. The relief or back pressure of pressure regulating device 46 is set at a level less than the lubricant injection pressure (i.e., inlet port 36), the pump pressure (i.e., cylinder 24 of fluid end 12), and greater than the pressure required for lubricant 34 to be disposed in voids 62.

In one example of operation of an embodiment of a lubrication system 32 and plunger pump 10, pressurized lubricant 34 is plumbed to stuffing box 28 through a one-way check valve 40. Depicted packing gland 30 has a clearance volume that allows for variance in the size of packing set 52 as plunger 16 strokes. The packing 56, 58 compresses during the power stroke and relax during the suction stroke of plunger 16. If lubricant 34 is injected just prior to a power stroke, packing gland 30 will have much less clearance volume (e.g., voids 62) than needed for the coming compression cycle. When packing set 52 is compressed lubricant 34 is expelled from voids 62 and flows through packing set 52 and discharged through discharge line 42 and pressure regulating device 46. For example, according to one embodiment of a well service plunger pump, the cracking pressure of device 46 is set at about 20 psi, to allow the lubricant expelled from voids 62 to be discharged through discharge line and avoiding damage to packing gland 30 and while maintaining sufficient pressure in packing gland 30 to maintain a sealing contact with plunger 16.

Advantages of the inventive system method relative to conventional plunger pump lubrication systems may include: preventing the packing (e.g., seal rings) from unloading during the power stroke as excess lubricant travels the path of least resistance, thereby reducing nibbling of the header ring; eliminating the need for reversing the orientation of the wiper seal respective of the phase (e.g., viscosity, density, etc.) of the lubricant utilized in a positive displacement lubrication system; eliminating and/or reducing the lubricant bypassing the seal; minimizing the volume of lubricant discharged to the atmosphere; eliminating the need for a drain pan; increasing the life of the packing seals; and eliminating over pressuring of the packing gland when priming.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.

Claims

1. A positive displacement plunger pump, the pump comprising:

a plunger reciprocally disposed through a packing gland, the packing gland comprising an inlet and an outlet;

a pressurized lubricant fluidicly connected to the packing gland at the inlet;

a pressure regulated discharge device fluidicly connected to the packing gland at the outlet.

2. The pump of claim 1, wherein the pressure regulated discharge device comprises a relief pressure less than the pressure of the pressurized lubricant at the inlet.

3. The pump of claim 1, further comprising a containment vessel fluidicly connected to the discharge through the pressure regulated discharge device.

4. The pump of claim 1, wherein the pressure regulated discharge device is a relief valve.

5. The pump of claim 1, wherein the packing gland comprises seal rings.

6. The pump of claim 1, wherein the packing gland comprises seal rings and a header ring.

7. The pump of claim 1, wherein the packing gland is a non-adjustable packing gland.

8. The pump of claim 1, wherein the packing gland comprises voids formed between adjacent seal members.

9. The pump of claim 1, wherein the packing gland is a non-adjustable packing gland comprising voids formed between the adjacent seal members, wherein the pressure regulated discharge device comprises a relief pressure less than the pressure of the pressurized lubricant at the inlet.

10. The pump of claim 9, further comprising a containment vessel fluidicly connected to the discharge through the pressure regulated discharge device.

11. A method comprising:

injecting a lubricant under pressure into a packing gland through which a plunger is reciprocating; and

discharging the lubricant from the packing gland in response to an outlet pressure greater than a selected relief pressure.

12. The method of claim 11, wherein the relief pressure is greater than a compression pressure necessary to maintain seal elements of the packing gland in sealing contact with the plunger.

13. The method of claim 11, wherein the discharging comprises discharging the lubricant into a containment vessel.

14. The method of claim 11, wherein the injecting the lubricant comprises injecting the lubricant through a stuffing box.

15. The method of claim 11, wherein:

the relief pressure is greater than a compression pressure necessary to maintain seal elements of the packing gland in sealing contact with the plunger; and

the discharging comprises discharging the lubricant into a containment vessel.