CN108730087B

CN108730087B - Liquid pump for inhibiting cavitation

Info

Publication number: CN108730087B
Application number: CN201810330906.8A
Authority: CN
Inventors: A·斯特克林; J·卡尔森; D·沃恩; R·帕兰杰普; D·易卜拉欣; G·考克斯; Z·李; R·欣里希森
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2017-04-24
Filing date: 2018-04-13
Publication date: 2022-05-27
Anticipated expiration: 2038-04-13
Also published as: DE102018109618A1; CN108730087A

Abstract

A liquid pump usable with a fuel system, such as a common rail fuel system, includes a valve assembly having a valve block with an axial alignment member, a dead volume, and vapor distribution flow passages for inhibiting cavitation. The inlet valve meters the flow of liquid into the pump for pressurization by a plurality of reciprocating plungers operated by a rotating camshaft.

Description

Liquid pump for inhibiting cavitation

Technical Field

The present invention relates generally to inlet metering liquid pumps with control output via an inlet throttle valve, and more particularly to inlet metering liquid pumps having a valve train designed to inhibit cavitation.

Background

In one type of high pressure liquid pump, the output from the pump is controlled by throttling the inlet using an electronically controlled metering valve. Cavitation bubbles are therefore generated when the output of the pump is controlled to be below the volume displaced by each reciprocation of the pump plunger. One application of such pumps is in fuel systems that utilize a common rail and a high pressure fuel pump to pressurize a rail. In this particular example, the engine directly drives the pump and the output from the pump is controlled by varying the inlet flow area via a throttle.

When the inlet throttle valve reduces the flow area to the plunger cavity, cavitation bubbles may be generated near the throttle valve, or potentially elsewhere, which travel to the plunger cavity, occupying a portion of the volume generated by retracting the plunger of the pump. Cavitation erosion may occur when cavitation bubbles collapse near the surface. In some instances, cavitation erosion may occur at undesirable locations, such as near an inlet passage or valve seat. Depending on where and how much cavitation damage occurs, pump performance can be compromised and perhaps more importantly, the eroding particles can find their way into the fuel injector, which can cause more serious problems.

U.S. patent 8,202,064B2 to Tian et al relates to a meter-in control liquid valve with features to avoid cavitation damage. Tian et al propose a cavitation flow regulator of a particular shape and size extending from the valve member in the passive inlet check valve. A flow-through pattern is created significantly through the valve in a manner that encourages cavitation bubbles to collapse away from the surface, which can result in unacceptable cavitation damage to the pump. While Tian et al appear to provide an improvement over the prior art, other developments involving cavitation suppression are also welcome in the industry.

Disclosure of Invention

In one aspect, a valve assembly for a liquid pump includes a valve body having a fluid inlet and a fluid outlet formed therein. The valve body includes a valve set forming an inlet valve seat and an outlet valve seat, and each of the inlet valve seat and the outlet valve seat is fluidly positioned between the fluid inlet and the fluid outlet. An inlet check valve is positioned at least partially within the valve block and is movable between a closed position blocking the inlet valve seat and an open position. An outlet check valve is positioned at least partially within the valve block and is movable between a closed position blocking the outlet valve seat and an open position. The plunger is movable within the valve body between a retracted position and an advanced position. The inlet check valve, the outlet check valve, and the plunger define a common axis extending through the valve block, and the inlet check valve is axially located between the outlet check valve and the plunger. The valve body further defines therein a pump chamber that receives the plunger, an inlet chamber within the valve block, and an outlet chamber within the valve block. The centers of each of the pump chamber, the inlet chamber and the outlet chamber are located on a common axis. The valve assembly further comprises a flow-through channel for diverting pumped liquid between the fluid inlet and the fluid outlet. The plurality of flow-through passages are arranged in a first parallel group extending between the inlet chamber and the pump chamber and having a first circumferential distribution about the common axis, and in a second parallel group extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.

In another aspect, a valve block for a liquid pump includes an inlet piece having formed therein an inlet valve seat, a fluid inlet, and a plurality of inlet fluid passages extending between the fluid inlet and the inlet valve seat. The valve block further includes an outlet member positioned on a first side of the inlet member, with an outlet valve seat formed within the outlet member, and a fluid outlet. The valve seat further includes a pumping member positioned on the second side of the inlet member such that the inlet member is sandwiched between the pumping member and the outlet member, and includes an inlet check valve positioned at least partially within the inlet member. The inlet check valve is movable between a closed position blocking the inlet valve seat and an open position. The valve block further includes an outlet check valve positioned at least partially within the outlet member and movable between a closed position blocking the outlet valve seat and an open position. The inlet member, the outlet member and the pumping member define a common axis. Each of the inlet check valve and the outlet check valve is movable along a common axis between the respective closed position and the open position. The valve seat further forms an inlet chamber between the inlet member and the pump member, an outlet chamber between the inlet member and the outlet member, a pump chamber and a plurality of flow passages. The plurality of flow-through passages are arranged in a first parallel group extending between the inlet chamber and the pump chamber and having a first circumferential distribution about the common axis, and in a second parallel group extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.

In yet another aspect, a liquid pump includes a pump housing with a pump inlet and a pump outlet formed therein, and an inlet metering valve. The valve assembly is positioned within the pump housing and includes a valve body having a valve set forming an inlet valve seat and an outlet valve seat. The liquid pump further includes an inlet check valve positioned at least partially within the valve block and movable between a closed position blocking the inlet valve seat and an open position. An outlet check valve is positioned at least partially within the valve block and is movable between a closed position blocking the outlet valve seat and an open position. The plunger is movable within the valve body between a retracted position and an advanced position. The inlet check valve, the outlet check valve, and the plunger define a common axis extending through the valve block, and the inlet check valve is axially located between the outlet check valve and the plunger. The valve body further defines therein a pump chamber for receiving the plunger, an inlet chamber within the valve block, and an outlet chamber within the valve block, and the pump chamber, the inlet chamber, and the outlet chamber are all centered on a common axis. The liquid pump further comprises a plurality of flow-through passages for displacing pumped liquid through the valve block, the plurality of flow-through passages being arranged in a first parallel set extending between the inlet chamber and the pump chamber and having a first circumferential distribution around a common axis, and in a second parallel set extending between the inlet chamber and the outlet chamber and having a second circumferential distribution around the common axis.

Drawings

FIG. 1 is a side cross-sectional view of a liquid pump in a liquid system according to one embodiment;

FIG. 2 is an end sectional view through the liquid pump shown in FIG. 1;

FIG. 3 is a side sectional view through a portion of the liquid pump of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view through a portion of the liquid pump of FIGS. 1-3 in a plurality of cross-sectional planes;

FIG. 5 is a cross-sectional view at a cross-sectional plane similar to FIG. 4;

FIG. 6 is an axial end view of an inlet piece within a valve block according to one embodiment; and is

Figure 7 is an axial section through the inlet piece.

Detailed Description

Referring to FIG. 1, a fluid system 10, such as a fuel system for an internal combustion engine, is shown. The fluid system 10 (hereinafter "system 10") may include a reservoir 12 for containing pressurized fluid, such as a common rail or the like (hereinafter "common rail 12") configured to contain pressurized fluid and supply the pressurized fluid to a plurality of fluid delivery devices or fuel injectors 13. The fluid system 10 may include a fuel system configured for use with a direct injection compression ignition diesel engine, for example, wherein each of the fuel injectors 13 is positioned at least partially within an engine cylinder. For example, the common rail 12 may include a single bore, an elongated pressure vessel, or a plurality of individual fluid accumulators coupled together in a so-called daisy-chain arrangement or other configuration. The system 10 also includes a liquid supply, such as a fuel tank 14, and a low pressure transfer pump 16 coupled to the fuel tank 14 and configured to transfer fuel to a high pressure liquid pump 20 through an inlet valve 18. The inlet valve 18 may include an inlet throttle valve that may be adjusted to vary the flow area to the liquid pump 20. The change in flow area meters the fuel flow to the pump 20 such that the pump 20 pressurizes only the required amount of fuel to maintain or achieve the desired fluid pressure on the common rail 12.

Those skilled in the art will be familiar with the concept of an inlet metering pump in the present context. Inlet valve 18 may be part of pump 20 and within pump 20, or potentially positioned upstream of pump housing 22 of pump 20. A suitable design for the inlet valve 18 is known from the aforementioned united states patent 8,202,064B2, commonly owned by Tian et al, although the invention is not so limited. The person skilled in the art will also be familiar with cavitation phenomena associated with inlet metering pumps. As will become more apparent in the following description, the configuration of pump 20 to suppress cavitation may be designed according to a number of design concepts that may be used together or independently of each other. Design concepts include, but are not limited to, robust symmetrical mechanical design, component positioning and placement, vapor distribution, reduced hydraulic stiffness and propensity for production and/or collapse of vapor bubbles towards areas within the liquid pump where cavitation damage is relatively insensitive.

The pump 20 includes a rotatable camshaft 24 positioned at least partially within the pump housing 22 and configured to be rotated by an engine transmission (not shown) in a generally conventional manner. Rotation of camshaft 24 results in reciprocating movement of a plurality of pumping mechanisms 26, each equipped with a cam follower 28 for a plunger 78 in a generally conventional manner. Each of the plurality of pump mechanisms 26 supplies pressurized fluid to a common fluid pressure space 30 (hereinafter "space 30"), and thereafter supplies pressurized fluid to the common rail 12 through a pump outlet 34 formed in the pump housing 22. Pump outlet 32 may be formed within pump housing 22 and supplied with fuel at a flow rate determined according to the flow area of inlet valve 18 as described herein.

In the illustrated embodiment, the pump housing 22 includes a plurality of housing pieces, namely a first housing piece 36, a second housing piece 38, and a third housing piece 39 in which the plurality of pump mechanisms 26 are disposed that define the space 30 and the pump outlet 34. It should be understood that the various housing configurations, including the number and design of the plurality of housing pieces, the number of pump mechanisms, and the paths of the various plumbing features may be different than shown. In addition, additional valves may be used, such as a check valve between the transfer pump 16 and the inlet valve 18 and/or a check valve between the pump outlet 34 and the common rail 12, but omitted from FIG. 1 for clarity of illustration. Fig. 2 shows an axial end view relative to camshaft 24, from which it can be seen that rotation of camshaft 24 causes the illustrated pump mechanism 26 to reciprocate up and down, drawing liquid into pump 20 and filling space 30 to supply pressurized liquid to common rail 12. The two pump mechanisms 26 in the illustrated embodiment generally reciprocate out of phase with one another, such as by a 180 degree out of phase difference.

Pump 20 further includes a valve assembly 40 associated with each pump mechanism 26. It should be understood that any singular reference herein to a component or assembly, such as the valve assembly 40 or the pump mechanism 26, is intended to similarly refer to any other such component for the pump 20 or other embodiments contemplated herein. The valve assembly 40 includes a valve body 42 positioned within the pump housing 22. Referring again to fig. 3, the valve body 42 has a fluid inlet 44 formed therein that communicates with another fluid inlet 46 formed by a valve block 60 of the valve body 42. The valve body 42 further includes a fluid outlet 48 also formed by a valve block 60. In the illustrated embodiment, the valve block 60 also includes an inlet piece 62 having formed therein an inlet valve seat 64, the fluid inlet 46, and a plurality of inlet fluid passages 66 extending between the fluid inlet 46 and the inlet valve seat 64. The valve block 60 also includes an outlet member 68 positioned on a first side of the inlet member 62. A valve seat 70 and a fluid outlet 48 are formed in the outlet member 68. The pumping member 72 is positioned on a second side of the inlet member 62 such that the inlet member 62 is sandwiched between the pumping member 72 and the outlet member 68.

An inlet check valve 74 having a biasing spring 75 coupled thereto is positioned at least partially within the valve 60 and at least partially within the inlet 62. The inlet check valve 74 is movable against the biasing force of the biasing spring 75 between a closed position blocking the inlet valve seat 64 and an open position unblocking the inlet valve seat 64. An outlet check valve 76 associated with a biasing spring 77 is positioned at least partially within outlet member 68 and is movable between a closed position blocking outlet valve seat 70 and an open position unblocking outlet valve seat 70. The plunger 78 is movable between the retracted position and the advanced position of the valve body 42 to draw liquid from the pump inlet 32 into the valve block 60 through the fluid inlet 46 and various other fluid passages and connections of the pump 20 and pressurize and deliver the liquid to the space 30 for delivery to the common rail 12 for injection into the engine cylinder.

It will be appreciated that with inlet valve 18 restricted to the inlet flow area of pump 20, drawing in liquid by retracting plunger 78 will tend to cause the fluid pressure of the liquid to drop to and below the pressure at which vapor bubbles are formed in the liquid, which must collapse and become pressurized. The collapse of these bubbles can be associated with the generation of high velocity microjets of liquid that can impinge on surfaces within the pump causing cavitation damage that essentially erodes the material forming the surfaces. Although cavitation can still occur during operation of the pump 20 in accordance with the present invention, the severity of damage cavitation is expected to be reduced and will tend in location to areas of the pump that are remote from surfaces susceptible to erosion damage.

Inlet member 62, outlet member 68, and pumping member 72 define a common axis 80. Each of the inlet check valve 74, the outlet check valve 76, and the plunger 78 may be movable along a common axis 80 between respective closed and open positions or, in the example of the plunger 78, between retracted and advanced positions. It has been found that arranging the substantially axially symmetric parts substantially coaxially as in the valve block 60 can have a number of advantageous effects, including improved symmetry and consistency of the liquid flow, the ability to match the contact part stiffness to avoid relative motion and thus reduce or avoid fretting damage during use, and the relative consistency of the parts deformation over time. For example, the "seat-in" phenomenon known in the art can be expected to occur in a relatively consistent pattern compared to alternative designs. It may be further noted that inlet member 62, which is axially sandwiched between outlet member 68 and pumping member 72, may axially position inlet check valve 74 between plunger 78 and outlet check valve 76. Also, arranging the valves as shown may result in a reduced amount of steam at or near the outlet check valve 76, specifically where the inlet check valve 74 is spatially and hydraulically arranged in sequence, while the outlet check valve 76 is axially remote from the plunger 78. In the illustrated embodiment, the inlet valve seat 64 comprises a flat seat and the outlet valve seat 70 comprises a conical seat, each of which is centered on the common axis 20. The relationship between the above and other design features and cavitation are discussed further below.

It may be further noted that in the illustrated embodiment, the valve body 42 includes an outer valve body member 50 and an insert 52 positioned within the outer valve body member 50. The insert 52, together with the member 50, defines a central bore 54 and an annular space forming the fluid inlet 44. In this context, the terms "fluid inlet" and "inlet annulus" may be used interchangeably. The insert 52 further includes a plurality of inlet apertures 56 formed therein that extend between the fluid inlet or inlet annulus 44 and the central aperture 54. The inlet port 56 extends generally radially and feeds an inlet passage 58 extending axially within an inlet piece 62. The valve seat 60 is positioned within the central bore 54 such that the inlet annular space 44 is in fluid communication with the inlet bore 56 and the fluid inlet 46 in the inlet piece 62. A plurality of inlet fluid passages 66 in the inlet piece 62 extend radially inward from the fluid inlet 46 to the inlet passage 58.

As indicated above, the liquid pump 20, and in particular the valve block 60, is configured for reduced hydraulic stiffness, which may reduce the rate of pressure rise relative to time or "dp/dt" during a pumping or pressurizing stroke, as described further below. To this end, the valve block 60 further defines an inlet chamber 82 between the inlet member 62 and the pump member 72, an outlet chamber 84 between the inlet member 62 and the outlet member 68, and a pump chamber 86 between the pump member 72 and the insert 52. As shown in fig. 3, the plunger 78 is movable within a travel distance 100 defining a working volume. In one embodiment, the plunger 78 defines a working volume, and the depicted inlet chamber 82, outlet chamber 84, and pumping chamber 86 along the plurality of flow-through passages 90 define a combined volume that is greater than the working volume. The combined volume may be about two to about three times the working volume, and more specifically may be about 2.1 times the working volume. Since dead volume may reduce pump efficiency by some means, a balance is struck, within the scope described, between efficiency and leveling off of the pressure rise to inhibit cavitation without unduly sacrificing efficiency, although the invention is not so limited.

The valve block 60 also defines a plurality of flow passages 90. The flow-through passages 90 are each circular, are arranged in a first parallel set 92 extending between the inlet chamber 82 and the pump chamber 86 and have a first circumferential distribution about the common axis 80, and in a second parallel set 94 extending between the inlet 82 and the outlet chamber 86 and have a second circumferential distribution about the common axis 80. The flow area formed by the first parallel set 92 may be smaller than the flow area formed by the inlet check valve seat 64. In one embodiment, the flow-through area may be reduced by a factor of about 50%. It has been observed that providing a larger downstream flow area during filling can bias the generation of vapor bubbles toward the pump chamber 82 rather than toward the valve seat or other area, thereby making the collapse of the vapor bubbles less cumbersome or more manageable.

Referring now again to fig. 4, 5, 6, and 7, in one embodiment, the total number of flow channels 90 in the first parallel group 92 is equal to the total number of flow channels 90 in the second parallel group 94. It can be seen that each of the flow-through channels 90 in the first and second

parallel groups

92, 94 have a uniform size, shape and regular distribution. Each flow-through channel 90 is also positioned a uniform radial distance from the common axis 80. The flow-through passages 90 in the

sets

92 and 94 may also be located within the spatial envelope defined by the inlet chamber 82, the outlet chamber 84, and the pump chamber 86. The flow-through passages 90 within the first group 92 may have a staggered arrangement with the flow-through passages 90 of the group 94 about the common axis 20. The total number of flow-through channels 90 in each of the

sets

92 and 94 may be eight.

Industrial applicability

Those skilled in the art will appreciate that by definition all inlet metering pumps will have vapor generation, and that the vapor will necessarily break causing the pressure to rise and begin pumping liquid. Generally, to achieve minimal or zero erosion in the inlet metering pump, the bubbles must be broken at a sufficiently low energy level so that the bubble breakage does not produce a jet of energy high enough to cause damage to the surface. The bubble collapse energy tends to be higher when the bubble collapses in areas of high ambient pressure. The relatively rapid rise in pressure from below the vapor pressure to well above the vapor pressure can result in bubbles being trapped in areas of high ambient pressure. Thus, when these vapor bubbles collapse, they can be problematic and produce cavitation damage. At least at the beginning of pumping, a relatively fast pumping rate and a relatively large plunger may be associated with a relatively large dp/dt.

As described above, dead volume may result in less system stiffness due to the fluid bulk modulus that reduces dp/dt. Furthermore, the uniform and consistent distribution, identical shape, and identical dimensions of the flow-through channels 90 result in fluid pumping through the flow-through channels 90 with minimal generation of recirculation zones, eddies, or other non-uniform or non-laminar flows that may be associated with cavitation. The total number of flow-through passages being eight, circular, uniformly radially spaced from common axis 80 and uniformly circumferentially distributed about common axis 80 are believed to cause the liquid to tend to move as a whole relatively uniformly during the pumping action of pump 20. Furthermore, the distributed, uniformly sized, uniformly arranged and uniformly shaped flow channels distribute the vapor such that no one local area is specifically damaged by the bubble. The smaller flow area of the flow passage 90 relative to the opening of the inlet valve seat 64 may also assist in biasing the location of steam generation and/or rupture toward the pump chamber 86 and thereby avoid rupture at critical valve seats or structural hot spots. These and other methods described herein may maximize the potential life of the pump even though some background levels of erosion are unavoidable.

Also, as indicated above, the axial stacking of the substantially axisymmetric parts allows the hardnesses to be matched, thus minimizing relative movement of the mating members on the sealing surfaces and reducing or eliminating fretting. In the high pressure and high cycle environment of pump 20, the symmetric center valve tends to deform unevenly around the 360 degree seat, ensuring a stable seal is maintained even after small break-ins or debris related wear. It has been observed that ensuring a stable seal, particularly in outlet valves or lead-out valves such as outlet check valve 76, helps limit erosion. Valve seat leakage between pumping events can produce high velocity flows at high cavitation numbers, and vapor bubbles cause these flows to collapse at the beginning of the next pumping event and cause erosion damage near the leakage seat.

Axially positioning the inlet check valve 74 between the top of the pump chamber 86 and the outlet check valve member 76 provides a flow path that further inhibits cavitation. In certain earlier references, the steam bubbles that form can be traced to the furthest position from the prime mover, which is typically a lead-out valve. Without the design provisions set forth herein that are known to this phenomenon, vapor bubbles may collapse at this location. It is contemplated that inlet valve seat 64 may comprise a flat seat, minimizing the flow area for a given size of valve production. Such a design may result in or enhance downstream confinement to the target valve seat and does not rely on a knife to effect a seal, which makes the design more resilient to debris damage.

This description is intended for illustrative purposes only and should not be construed to limit the scope of the present invention in any way. Accordingly, it will be appreciated by those skilled in the art that changes could be made to the disclosed embodiments without departing from the full and fair scope and spirit of the invention. Other aspects, features and advantages will be apparent upon examination of the attached drawings and appended claims. As used herein, the article "a" is intended to include one or more items, and may be used interchangeably with "one or more". The term "one" or similar language is used when it is intended to refer to only one item. Likewise, as used herein, the term "having" and the like are intended to be construed as open-ended terms. Further, the term "based on" means "based, at least in part, on" unless explicitly indicated otherwise.

Claims

1. A valve assembly for a liquid pump, comprising:

a valve body having a fluid inlet and a fluid outlet formed therein, and including a valve block forming an inlet valve seat and an outlet valve seat, each fluidly positioned between the fluid inlet and the fluid outlet;

an inlet check valve separate from the valve body, the inlet check valve positioned at least partially within the valve block and movable relative to the valve block between a closed position blocking the inlet valve seat and an open position;

an outlet check valve positioned at least partially within the valve block and movable between a closed position blocking the outlet valve seat and an open position;

a plunger movable within the valve body between a retracted position and an advanced position;

the inlet check valve, the outlet check valve, and the plunger defining a common axis extending through the valve block, and the inlet check valve being axially located between the outlet check valve and the plunger;

the valve body further having formed therein a pumping chamber that receives the plunger, an inlet chamber within the valve block, and an outlet chamber within the valve block, and each of the pumping chamber, the inlet chamber, and the outlet chamber being centered on the common axis; and

a plurality of flow-through passages formed in the valve body for diverting pumped fluid between the fluid inlet and the fluid outlet, the plurality of flow-through passages being arranged within a first parallel set defined by the valve block and having a first circumferential distribution about the common axis fluidly connecting the inlet chamber to the pump chamber and within a second parallel set defined by the valve block and having a second circumferential distribution about the common axis fluidly connecting the inlet chamber to the outlet chamber.

2. The valve assembly of claim 1, wherein a total number of the flow-through channels in the first parallel set is equal to a total number of the flow-through channels in the second parallel set, and wherein the first circumferential distribution is different from the second circumferential distribution such that the first parallel set and the second parallel set have a staggered arrangement about the common axis; and is

Wherein the flow area formed by the first parallel set is smaller than the flow area formed by the inlet check valve seat.

3. The valve assembly of claim 2, wherein the plunger defines a working volume, and the inlet chamber, the outlet chamber, the pumping chamber, and the plurality of flow-through passages define a combined volume that is greater than the working volume;

wherein the combined volume is 2 to 3 times the working volume; and is

Wherein the total number of flow-through channels of each of the first and second parallel groups is eight, and wherein each of the first and second parallel groups is evenly distributed according to a corresponding first or second circumferential distribution at a uniform radial distance from the common axis.

4. The valve assembly of claim 1, wherein the valve body further comprises an outer housing piece and an insert defining a central bore, and the insert forms an inlet annular space with the outer housing and has a plurality of inlet bores formed therein, and the plurality of inlet bores extend between the inlet annular space and the central bore, and wherein the valve seat is within the central bore such that the fluid inlet is in fluid communication with the plurality of inlet bores; and is

Wherein the valve seat comprises an inlet member having a plurality of inlet fluid passages extending radially inwardly from the fluid inlet, an outlet member and a pumping member, wherein the inlet chamber is defined in part by the inlet member and in part by the pumping member, the outlet chamber is defined in part by the inlet member and in part by the outlet member, and the pumping chamber is defined in part by the pumping member and in part by the insert member.

5. A valve manifold for a liquid pump, comprising:

an inlet piece having formed therein an inlet valve seat, a fluid inlet, and a plurality of inlet fluid passages extending between the fluid inlet and the inlet valve seat;

an outlet member positioned on a first side of the inlet member, the outlet member having an outlet valve seat and a fluid outlet formed therein;

a pumping member positioned on a second side of the inlet member such that the inlet member is sandwiched between the pumping member and the outlet member;

an inlet check valve positioned at least partially within the inlet and movable between a closed position blocking the inlet valve seat and an open position;

an outlet check valve positioned at least partially within the outlet member and movable between a closed position blocking the outlet valve seat and an open position;

said inlet member, said outlet member and said pumping member defining a common axis, and each of said inlet check valve and said outlet check valve being movable along said common axis between respective closed and open positions;

the valve seat further forming an inlet chamber between the inlet member and the pump member, an outlet chamber between the inlet member and the outlet member, a pump chamber and a plurality of flow passages; and

the plurality of flow-through passages are arranged in a first parallel group extending through the pumping member between the inlet chamber and the pumping chamber and having a first circumferential distribution about the common axis, and in a second parallel group extending through the inlet member between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.

6. The valve manifold of claim 5, wherein a flow area formed by the first parallel set is smaller than a flow area formed by the inlet check valve seat;

wherein the total number of flow-through channels in the first parallel group is equal to the total number of flow-through channels in the second parallel group; and is

Wherein each of the plurality of flow-through passages is positioned at a uniform radial distance from the common axis, within a spatial envelope defined by the inlet chamber, the outlet chamber, and the pump chamber, and wherein the flow-through passages in the first parallel group are staggered from the flow-through passages in the second parallel group about the common axis.

7. The valve manifold of claim 5, wherein the inlet valve seat comprises a flat seat and the outlet valve seat comprises a conical seat, and the center of each of the inlet and outlet valve seats is on the common axis.

8. A liquid pump comprising:

a pump housing having a pump inlet and a pump outlet formed therein;

an inlet metering valve configured to vary a flow area of the pump inlet;

a first valve assembly within the pump housing and comprising a valve body having a fluid inlet and a fluid outlet formed therein and a valve block forming an inlet valve seat and an outlet valve seat;

an inlet check valve positioned at least partially within the valve block and movable between a closed position blocking the inlet valve seat and an open position;

the valve body further having formed therein a pumping chamber that receives the plunger, an inlet chamber within the valve block, and an outlet chamber within the valve block, and the pumping chamber, the inlet chamber, and the outlet chamber are all centered on the common axis; and

a plurality of flow-through passages for diverting pumped liquid through the valve block between the fluid inlet and fluid outlet, arranged in a first parallel set extending between the inlet chamber and the pump chamber and having a first circumferential distribution about the common axis, and in a second parallel set extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis;

wherein the valve body further comprises an outer housing piece and an insert defining a central bore, and the insert forms an inlet annular space with the outer housing and has a plurality of inlet bores formed therein, and the plurality of inlet bores extend between the inlet annular space and the central bore, and wherein the valve seat is within the central bore such that the fluid inlet is in fluid communication with the plurality of inlet bores; and is

9. The liquid pump of claim 8, further comprising a second valve assembly substantially identical to the first valve assembly, and further comprising a first cam follower to which the plunger of the first valve assembly is coupled and a second cam follower to which the plunger of the second valve assembly is coupled;

wherein the pump housing forms a common fluid pressure space therein, each of the first and second valve assemblies being fluidly positioned between the common fluid pressure space and the pump inlet; and is

Wherein the plunger defines a working volume and the inlet chamber, the outlet chamber, the pumping chamber and the plurality of flow-through passages define a combined volume that is 2 to 3 times the working volume.

10. The liquid pump of claim 8, wherein the total number of flow-through channels of each of the first and second parallel groups is eight, and wherein each of the first and second parallel groups is evenly distributed according to a corresponding first or second circumferential distribution of consistent radial distance from the common axis; and is