Injecting apparatus

The present invention also provides an injecting system comprising an injecting apparatus according to the first aspect of the invention, a fluid pressure relief path through which fluid pressure in the low pressure chamber can be controllably relieved to permit and

<img file="AU666331B2_D0001.tif" />

I

<img file="AU666331B2_D0002.tif" />

i • =·«· control movement of the piston means, and an associated fluid pressure governor means, the governor means being selectively controllable to control the fluid pressure in the low pressure chamber by selectively preventing or progressively limiting relief of pressure from the low pressure chamber through the fluid pressure relief path in response to movement of the piston means. The governor means may include a flow restriction means in the fluid pressure relief path to selectively control the cross sectional area of the fluid pressure relief path, the flow restriction means having an associated drive means so as to drive the flow restriction means to vary the cross sectional area of the relief path.

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In the injecting system, the governor means may further include a back pressure valve located in the fluid pressure relief path downstream of the flow restriction means, the back pressure valve being operative to maintain a predetermined minimum back pressure in the fluid pressure relief path by only opening when the predetermined minimum back pressure is exceeded.

The fluid pressure relief path may include a pressure compensating means which includes a restriction and varying means for varying the size of the restriction in response to changes in fluid pressure downstream thereof, the varying means being operative to reduce the area of the restriction to maintain a predetermined pressure downstream of the pressure compensating means. In this arrangement, the pressure compensating means may comprise a chamber which communicates with the low pressure chamber, the pressure compensating means further including a shuttle valve responsive to the pressure differential between the fluid pressure in said chamber and a point further downstream in the fluid pressure relief path and being operative in response to an inci ease in the pressure differential to reduce the area of ό

5a the restriction and thereby retard pressure relief from the chamber to the point further downstream.

The injecting system may further include a controllable damper means in communication with the fluid pressure relief path, the damper means including a movable damper member responsive to a pressure increase in the fluid pressure relief path to yield so as to thereby relieve pressure in the fluid pressure relief path, the damper means further including an adjustable limiting means associated with the movable damper member to controllably limit the extent of yielding movement, the limiting means thereby effectively ί ί ' · &lt; ί ' t ί i &lt;4 ti t

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<img file="AU666331B2_D0003.tif" />

determining the pressure relief provided by the damper means. The movable damper member mav comprise a resilient damper disc which defines one wall of a chamber which is in communication with the fluid pressure relief path, the limiting means comprising a limiting stop which is adjustable so as to be contacted by the damper disc.

In the injecting system of one possible embodiment the fluid pressure relief path may include a high speed solenoid valve operative to open and close the fluid pressure relief path in response to actuation signals, the governor means being located downstream of the solenoid valve and being operative to adjustably limit in continuous increments the flow of fluid through the fluid pressure relief path.

Possible and preferred features of the present invention will now be described with particular reference to the accompanying drawings. However, it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention. In the drawings:

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WO 93/04275

PCT/AU92/00453 _: i

<td> Fig. 1 shows a</td><td> cross</td><td> sectional</td><td> view</td><td> through</td><td> an injector</td>

<td> according to the present</td><td colspan="2"> invention.</td><td></td><td></td><td></td>

<td> Fig. 2 shows a</td><td> cross</td><td> sectional</td><td> view</td><td> through</td><td> one possible</td>

<img file="AU666331B2_D0006.tif" />

arrangement of a governor or accelerator for use in controlling 5 operation of the injector,

Fig, 3 is a cross sectional view through an alternative construction of injector according to the present invention.

Fig. 4 is a cross sectional view through the rear portion of a further possible construction of injector showing vai ious means l'oi 10 enabling control of the injector operation.

Fig. 5 is a plan view of the detailed section marked A” ii.· ' Fig. 4. and ,

Fig. 6 is a sectional view along the line VI - VI in Fig. 4.

Referring to Fig. 1, the injectoi includes a body 10 which 15 comprises a front body part 11 which can for example have a threaded end 12 for engagement in a threaded port associated w’ith an engine, and a rear body part 13. An inlet 15 is provided in the bodv 10. the . inlet 15 having anon-return valve 16 operated bv spring 17. In use, fuel is supplied or induced under low pressure into the inlet 15 20 sufficient to overcome the action of spring 17. The strength of • spring 17 is not critical. The fuel pressure can be relative]', low so that high pressure fuel lines arc not required.

Au outlet 20 has an associated nou-return valve 21 acting b&gt; means of spring 22. the strength of which is not critical. Kith this 25 arrangement, fuel can continuously be pumped or induced under lot.

pressure into inlet 15, through passage 25 and out through outlet 20. This continuous fuel flow can provide cooling although supplementary cooling could be provided.

The injector includes a low pressure piston 30 slidable in th'^j30 front body 11 when engine cylinder pressure acts on the front face 31. Compression ring 32 and oil scraper ring 33 are provided for conventional purposes. Screwed to the low pressure piston 30 is .i high pressure piston 35. The piston assembly 30, 35 moves within the body 10 against the action of main spring 36. The force applied b'· 35 main spring 36 determines, in part, whether the piston assembly 30.

will move under the action of cylinder pressure on face 31. Alsu, the main spring 3*,·. is located m a low pressure chambei 37 which i.·

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PCT/AU92/00453

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in fluid communication through space 3b with the passage 25 arid through valve 21 with th° outlet 20 so that the fluid pressure in low pressure chamber 37 resisting movement of the piston assembly 30, 35 can be relatively low, subject to control t.o be described later.

A possible variation of the preferred construction illustrated and described is the replacement of the mail· spring 36 with a pneumatic or other biasing means.

Tin- high pressure piston 35 has an extension -&lt;0 of relatively small cross sectional· area which travels within a bin'- Al provided 10 within a high pressure body 42. The high pressure body 42 comprises a base section 43 and a high pressuie barrel 44 in which the extension 40 travels. The base section 43 and high pressuie barrel 44 ate secured togethet and define a high pressuie chanibei 45 in which fuel is compressed tu high pressuie bv the extension 40 of the 15 high pressure piston 35. Non-retum valve 4Λ operated by a spring 47 allows fuel to enter the high pressuie chambei 45 from the passage 25 upon retraction of the high pressure piston extension 40 in the bore 4'1. The strength of spiiug 47 is not critical.

In the extension 40 there is provided a bleed bore 50 and extending through the high pressure barrel 44 Is a bleed bore 51 which opens into the low pressure chanibei 37. If the stioke of tin· ' piston assembly 30, 3 is sufficient, foi the bleed bore 50 to align with the bleed bore 51, the fuel withii' 1'· high press'!!' chamber 45 is immediately placed in communication with the low piessure chan.bei

37 and the fuel pressure iri high pressure ehambei 45 will immediately drop so that there will to continue as will b*·· be insufficj ent. pressure foi fuel injection described late),

Thus t&gt;·” longitudinal separation between the bleed bore 50 and boip 51 effectively during one defines the maximum fuel charge that can be injecled of the piston assembly 30, limits the speed of running of the associated engine predetermined maximum determined'by the maximum fuel charge.

effectivelv stroke and this, in turn.

to cl

Running longitudinally through the extension 40 of the high pressure piston 3.5 is a fuel passage 55 along which pressurised fuel from the high pressure chamber 45 travels cis the piston assembly .30.

moves unaei the actio· of the cylinder pressure. The fuel passe non-retuii. deliver vaJv&gt; 56 which J.· shown testing against

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WO93/04275 ;0·

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·Λ

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PCT/AU92/00453 shoulder 57 under the action of spring 5¾. In operation, high pressure fuel moves valve 56 away from shouldei 57 against the action 'of spring 58. Fuel flows past the valve 56 only when it has moved sufficiently for the shoulder 59 of the valve to move past the end of passage 60 formed on the inside surface of the high pressure piston

35, With this arrangement, when delivery valve 56 is closing, fuel flow past the valve 56 is -stopped when the shouldei 59 reaches the end of the passage 60, after which th? valve 5'. continues to move bv a further limited extent until the valve 5o reaches snouldei 57.

This continued movement of valve 56 after the valve has closed off fuel flow relieves pressure on the downstream side of the valve 56 for a purpose which will be described latei,

The low pressure piston 30 has a delivery chamber 65 into which high pressuie fuel is introduced through bore 66 provided m the 15 spacer 67. At forward end of the deliverv chamber 65 is a delivery orifice 68 provided in an insert 69. The orifice 68 is shown closed bv needle type deliverv valve 70 which seats against the insert. 69 undei the action of deliver, spring 71. Wnen the pressure of fuel in the delivery chambei 65 is sufficiently great, the needle valve 70 20 moves against the action of delivery spring 71 and opens the orifice 68 and fuel is injected through the orifice 68 into the associated engine cylinder. The commencement of injection through orifice 6causes an immediate drop in fuel pressure in delivery chambf·;· ti auc the needle valve 70 will tend to cltse the orifice 68 again. This. 25 in turn, will allow pressure in delivery chamber 65 to rise and again open needle valve 70. This process continues so that the needle valve 70 opens and closes the orifice 68 at high speed. This action is known as buzzing of the delivery needle valve 70 and causes the fuel tu be injected through ori^f e 6S in waves and this is believed 30 to improve fuel combustion efficiency.

The needle valve 70 has a shank 75 which moves within a guide

76. The end 77 of the shank 75 remote from the delivery orifice 68 closes a control chamber 78. Control chamber 78 communicates through

<img file="AU666331B2_D0012.tif" />

V (aligned· bores 79, 80 provided in the spacer 67 and low pressure piston 30 respectivelj and through the spac? 51 around the outsid? of the low pressure piston 30 with the low pressure chamber 37. Thus the control chambei 78 is normally in communication with low pressuie

WO 93/04275

PCT/AU92/00453 fuel allowing the needle valve 70 and shank 75 to move away from the insert 69 to open the orifice 68 under the pressure of fuel in the •delivery chamber 65.

Referring to Fig. 2. there is shown an accelerator or governor means which enables control of the flow of fuel on the downstream side of the injector. In particular, in use, the governor means shown in Fig. 2 comprises a body 85 having a bore 86 which is in communication with the outlet 20 of the injector. The downstream end of the bore 86 is provided with a chamfered seat 87. I.ongitudinallj.

selectively movable within the bore 86 is a governor 90 which has a complementary chamfered shouldei 91 which can close against seat 87 tr completely close bore 86. The governor 90 has a shank 92 which extends into the bore 86 and is a close fit within the bore. The shank 92 has a groove 93 which tapers from the shoulder 91 to the upstream end 94 of the shank 92. The fuel can flow into the bore 86 along the groove 93 and between the shouldei 91 and seat 8? when the governor 90 is retracted longitudinally in the direction of arrow A.

If the governor 90 is retracted only slightly from the seat 87. flov. along the groove 93 is significantly restricted since the fuel must 20 flow through 'the shallowest end of the groove 93 where the seat 87 meets the bore 86 at point 95. If the governor 90 is retracted further in the direction of arrow A. greater flow past point 95 is possible because of the deepening of the groove 93 towards the end

94. Thus the selective retraction and insertion of the governor 90 from and into the bore 86 enables control of the pressure in low pressure chamber 37 of the injector, which in turn, can control the stroke of the piston assembly 30, 35. If the governor 90 is moved to contact the shoulder 91 against the seat 87, the fuel flow through outlet 20 of the injector is prevented and this will hydraulically lock the piston assembly 30, 35 against movement by blocking the pressure relief path for fuel from low pressure chamber 37.

The movement of the governor 90 in Fig. 2 can be achieved bv any suitable means such as a mechanical adjustment of the position of governor 90. Alternatively the governor 90 could be moved by a DC electric motor oi lineal motor enabling electronic control of the fuel injection. In this wav, it is possible to infinitely vary the fuel injection by .controlling governor 90 in a continuous maunei,

WO 93/04275

PCT/AU92/00453 thereby controlling continuously the low pressure side of the injector which in turn enables control of the point in an operating cycle at which movement of the piston assembly 30, 35 is allowed to commence. In general terms, the hydraulic control of the low 5 pressure side of the piston assembly 30, 35 of the injector enables precise control of the point of commencement of the stroke of the piston assembly 30. 35 which controls the amount of fuel injected, up to a maximum charge determined by the spacing of the bleed bore 50 and 51.

in operation of the injector in an internal combustion engine, the increasing pressure on the front face 31 of the low pressure piston 30 during the compression state of the engine will tend to move the piston assembly 30, 35 against the action of both the mam spring 36 and the fluid pressure m chamber 37. If the pressure relief from the low pressure chamber 37 through outlet 20 is permitted, the piston assembly 30, 35 retracts to compress fuel m high pressure chamber 45. The fuel flows through fuel passage 55, past delivery valve 56 and into delivery chamber 65. The pressure m chamber 65 causes the needle valve 70 to open against the action of both delivery spring 71 and the pressure in low pressure chamber 37 which, in turn, is in communication with control chamber 7S so that ’ fuel injection through orifice 68 commences.

Initially. fuel will

<td colspan="2"> since the</td><td> pressure in</td><td> the</td>

<td> 25 However,</td><td> in</td><td> the case</td><td> of a</td>

<td> ignition</td><td> of</td><td> the fuel</td><td> in</td>

<td> increase</td><td> in</td><td> cylinder p</td><td> ressi</td>

injected in relatively· large droplets engine cylinder is still lelativelv low. compression ignition engine, immediately the cylinder occurs, there is a rapid ure which acts on face 31 of the piston

30. This pressure jump immediately· causes a multiplication of the fuel injection pressure so that the fuel being injected through 30 orifice 68 at a greatly increased pressure will emerge in much smaller droplets which improves the combustion efficiency. The initial injection pressure jump may be from 4000 psi to 25000 psi.

The ratio of injection pressure to input pressure may be between 6:1 and 12:1.

It is possible to control the proportion of the total fuel charge which is injected at the initial relatively low pressure by adjustment, of the strength;· cf the mam spring 3v and the deliver'·

WO 93/04275

PCT/AU92/00453 spring 71. For example, increasing the strength of the main spring 36 retards the point of movement of the piston assembly 30. 35 thus delaying the commencement of injection and reducing the proportion of the fuel which is injected during the initial low pressure injection 5 stage prior to ignition. By adjustment of these spring forces, it is possible to affect the efficiency of combustion and hence control emissions. e.g. foi different cylinder sizes. The ratio of the high arid low pressures of injection is also controllable.

The maximum fuel charge is determined by the spacing of t.he 10 bleed bores 50, j1 which effectively also provides a maximum engine speed limiter. In particular, when the bleed bores 50 arid 51 align, tn·· fuel pressure in th- high pressure chamber 45 is immediately relieved through the bleed bores 50. 51 and this pressute drop is immediately conveyed to the delivery chamber 65 so that the needle valve 70 immediately closes.

The external control of the pressure relief through the outlet 20 of the injector, e.g. by means of the governor means shown in Fig. 2, riot onl&gt; controls the point of opening movement of the piston assembly 30,-35 but also controls the low pressure side in chamber 37 during an injection operation. If the pressure relief through outlet is retarded, the movement of piston assembly. 30, 35 it- limited by the lelief of pressuir in th· low pressure chanibei 37 and also the opening movement vaJyt- 70 is resisted bv the retard·· ¹ lelief of the shank hydraulic operation.

occurs

50, 51 drop.

pressure ii: contrul of th· needle lock up controls

Alternatively, the when the maximur.

align and cause

In either case.

an the valve 70.

Thu^c los pressure side termination of the fuel injection termination of the injection operation injected and the bleed bores immediate high pressure side ptessure needle valve 70 closes the

68.

delivery valve 56 also will immediately

The delivery orifice move towards

<td> its closed</td><td> position</td><td> undei</td><td> the</td><td> action of</td><td> spring 5^C.</td><td> so that, the</td>

<td> shoulder 59</td><td> reaches</td><td> the</td><td> end</td><td> of passage</td><td> 60 thus</td><td> closing off</td>

<td> communication</td><td> between</td><td> th·.·</td><td colspan="3"> high pressure chambei 45 and</td><td> the delivei·-</td>

<td> 35 chambe. 65.</td><td> Because</td><td> tiie</td><td> deliver</td><td> ;. valve 56</td><td> continues to</td><td> mov* beyond</td>

the point at which shoulder 59 reache.-· the end of passage 60. the fluid pressuie m deliver·, chamber 65 ca ; continue to be relieved

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WO 93/04275

<img file="AU666331B2_D0015.tif" />

preventing opening of needle valve 70 until high pressure is again built up in delivery chamber 65. These combined actions of hydraulic •lock up of the low pressure side or high pressuie side pressure relief, together with the two stage movement of the delivery valve 56 5 ensure immediate and positive termination of the fuel injection.

The injector shown m Fig. 3 is in most respects the same as the injector shown in Fig. 1 and the same reference numerals are used for corresponding parts.

Different feature.-:, in Fig. j include the modified needle valve

70 which, instead of a conical tip. includes a blunt nose portion 70a which substantially fills the sack 72 which is a small space immediate 1'· ups treat of the· orifice 6^:.. The fuel remaining m the sack 7'2 in prioi ' injectors was sometimes a cause of continued fuel introduction into the evlinder after the desired cut off point.

Also in Fig. 3. the spacer 67 is provided with a non-return valve 100 arranged to allow the flow from the control chamber 78 to the low pressure chamber 37 but preventing a shock loading at any time from being transmitted into the chambpi 78.

In Fig. 3, the inlet 15 is shown in a different location with a relatively small inlet valve 16 allowing fuel under low pressure to pass fro:. the inlet 15 tu an inlet manifold 102 which encircles tht bod'· 10 and enables fluid tu pass from the annular manifold spa?*· 103 through passages 106 to tin- low pressure chambei 37.

Also in Fig. 3, there is provided a high speed solenoid 105 having an associated valve member 106 arranged to selectively close the outlet 20. The solenoid 105 can be energised under the control of an electrical switching means 107 by means of which the time of commencement of injection u controllable and also the length of the period of injection is also controllable. In particular, the opening of the valve 106 by solenoid 105 under the control of the control means 107 enables the injection to commence. Prior to opening of the valve 106 the piston assemble 30, 35 is effectively hvdraulically locked ,,a'nst movement. Similarly , closing of the valve 106 will again lock the piston assembl¹· 30, 35 against movement therebv terminating the injection.

Downstrear. of the valve 106 there is an outlet jort 110 through which pressure relieving flo- can take piece when the valve 106 j.s

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PCT/AU92/00453 open.

the re enable

Associated with the is preferably provided selective control of outlet port 110 or downstream thereof an adjustable flow restriction means to the rate of pressure relieving flow through the outlet port 110, the adjustable flow comprising a governor arrangement such as shown in Fig. 2 restriction

Fig

A showns an alternative injector control arrangement located at arrangement relief path may be fror. the bodv 13 of the injector, separate unit connected low pressure chamber 37.

Fig. 4, pressure relief from the chamber although the control in the fluid pressure

In the embodiment m is provided through a fluid pressure relief path comprising a first chamber 120 which communicates with an intermediate chambei

121 through a pressure compensating means 122 comprising a restriction 123 (Fig. 5· shown m the form of a slot provided within sleeve 124, Inside the sleeve there is provided a shuttle valve member 125 having a head 126 which progressively closes oi opens the slot 123 as the shuttle valve 125 moves within the sleeve 124.

. The fluid pressure relief path also includes a downstream low pressure chambei 130. The fluid pressure in chamber 130, togethei 20 with the force of spring 131 opposes movement of the shuttle valve 125 under the influence of fluid pressure from the chamber 120 passed to the intermediate chamber 121. Howevei if the pressure diff . .ntial between intermediate chambei 121 ®nd low pressuim chambei 130 riser sufficiently, the shuttle valve 125 will move ano 25 the head 126 will restrict the pi assure relieving flow through the slot 123 thereby enabling the pressure in the intermediate chambei 121 to reduce by means of flow to low pressure chamber 130.

Interposed in the fluid pressure relief path between the intermediate chamber 121 and the low pressure chamber 130 is a 30 selectively controllable flow restriction means 135 which comprises a needle valve 136 having a tapered nose portion 137 located in the passage 13S extending between intermediate chamber 121 and low pressure chamber 130. The needle valve 136 is selectively movable b&gt; means of electrical or mechanical control means 139 so as to enable 35 selective control of the rate of pressure relief through the passage 13$. This, in turn, enables control of the injection rate.

Downstream of th* flow restriction means 13^: there is a non-returi: valve 140 v?hich functions to maintain a minimum back

WO 93/04275

PCT/AU92/00453 pressure determined by the force of spring 141 which is a function oi the spring itself and the position of adjustable seal 142 foi th'spring 141, At low idle speeds of an associated engine, the valve

140 determines the minimum back pressure. At higher engine speeds.

the valve 140 remains open substantially all of the time.

The system shown in Fig. 4 also provides a controllable damper illustrated more clearly in Fig. 6. The damper means 150 means 150, includes mounted in movable a dampei duct 153 with the dampei membei 151 illustrated as a damper dis;

chambei 152 which is in communication through intermediate chambei 121. The dampei disc 151 yields resiliently upon an increasing pressur·· in the intermediate chambei 121.

There is an adjustable stop membei 155 which is adjustable by means of set screw 156 to enable selective setting of the limit of resilient movement of the damper disc 151. By adjusting the position of the stop member 155, the idle setting oi speed of an associated engine can be effectively controlled. In particular, a relatively large gap between the stop member 155 and the damper disc

151 enables a larger other flov. limiting means or pressurt? relief limiting means become effective, thereby enabling a higher idle speed to be set.

The embodiment of t.he injector svste· shown in Figs. 4 to 6 and described above provides a great deal of eoiitru] over th? operation of th·· iujectoi . including cuntr·.! over th·· t i-.inr. o' the -1 a. · an··¹end of injection, the rate of injection, idb. speed, and even 25 variation in rate of injection within a single injection cvcle. The greater degree of control that is possible makes the injector syster particularly suitable for direct fired internal combustion engines.

The construction and arrangement oi the injectors and associated controllers illustrated and described with reference to the drawings enables accurate and repeatable control of the point of commencement of the injection, accurate and repeatable control of the charge of liquid which is injected during each injection cvcle, and accurate and repeatable point of termination of the injection. The thie- stage positive termination of injection makes th· inj-ctoi suitable for high speed two stroke engines.

Automatic pollution control is one benefit of using the eyimde) pressure tu develop the injection pressuie. In particular, if the engine c'vlinde. develops &lt;i fault, such as a broken pistoe

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<img file="AU666331B2_D0016.tif" />

ring, leading to a drop in pressure in the cylinder, the pressure drop will immediately prevent or at least reduce the charge of fuel that the injector will introduce into that cylinder . Thus the engine will exhaust less unburnt fuel compared to an engine where a full 5 charge continues to be injected into a faulty cylinder. This compensation also occurs in the case of normal wear of components so that pollution reduction and wear compensation results.

Another benefit of the injector is that it provides automatj; timing adjustment. Iri particular, as an associated engine increases 10 in running speed, ideally, the commencement of injection should be advanced in the operating cycle since the fuel needs a predetermined minimum time to burn completely regardless of the speed of the engine. With the injector of the present invention, as the engine piston commences the compression cycle, there is a faster build up of 15 pressure in the cylinder at higher engine speeds since the heat is not escaping as quickly from the engine as at lower speeds. This more rapid increase in pressure will automatically advance the commencement of injection to earliei points in thn engine cycle. This advancement can be In excess of l^r-' from initial setting to the

<img file="AU666331B2_D0017.tif" />

point of injection at maximum engine speed.

, .- furthei advantage of the preferred injectors described and

Illustrated is the lowered average combustion overall pressure which result&gt; from the new combustion mode. Th.is in turn can lead to the use of lighter components. The new combustion mode results from 25 the different phases of the combustion of the fuel. If a pressure versus time graph for a conventional engine were shown, the graph rises sharply to a peak and drops rapidly. With the injectors of the preferred embodiment, the control of the injected droplet sizes and the injection pressures enables control of the combustion process so 30 that the pressure time graph can have a relatively flat plateau so that, the area under the graph which relates to the work can be the same as conventional engines but the lower maximum pressure leads to less stress in the motor and the ability to use smaller or' lightei components .

Because the injectors describee and illustrated requires lov.

levels of lubrication du® to the absence of beating components, the injectors will function with a no wax diesel fuel making it possibltWO 93/04275

PCT/AU92/00453 to work in cold climates. Kith careful material selection, LPG can be directly used.

A further advantage of the preferred injector construction and operation is the ability to automatically prime the injector for a subsequent operation. By closing the external governor means, there is a hydraulic lock up of the low pressure side, and fuel will be stored in the delivery chamber 65 since the fuel cannot be. released valve 5u.

Thus. when the associated engine the first cycle of the associated engine will enable fuel under pressure in the delivery chamber 65 to be injected for commencing normal operation of the engine .

In the particular construction of injectors shown m the drawings, metal to metal contacts are used to provide sealing between immovable parts. For example, the front body 11 and rear body 13 are connected together with metal to metal contact between a sharp step 96 provided on the rear bodv 13 and a chamfered face 97 provided on the front body 11. This also applies tr&gt; connections between the spacer 67 and the low pressure piston 30. between the spacer 67 and the high pressure piston 35, and between the high pressure barrel 44 and the base section 43. These connections are modified Lenz ring

<td> seats and</td><td> provide</td><td colspan="3"> good sealing under high pressures.</td><td></td>

<td> Th“</td><td> valves.</td><td> j including the inlet v</td><td> ,ilv&gt;* 1</td><td> h ,</td><td> outlet valve 21,</td>

<td> lion-return</td><td> valve</td><td> 46, delivery valve 56</td><td colspan="2"> and the</td><td> needle valve 70</td>

<td> preferably</td><td> have</td><td> sealing contact between</td><td> the</td><td> val</td><td> ve members and</td>

<td> associated</td><td> seats</td><td> with an internal angle les:</td><td> s than</td><td> 90°</td><td> , and preferably</td>

<td> at about</td><td> 60°.</td><td> For example, the included</td><td> angle</td><td> in</td><td> the point of t Il-</td>

<td colspan="2"> needle valve 70</td><td> is preferably about 60°</td><td> . This</td><td> re</td><td> lative ]v shallow</td>

angle of seating has been found to provide good sealing at a wide range of fluid pressures.