NL2005057C2

NL2005057C2 - Sealing assembly, device provided with such assembly and method for sealing.

Info

Publication number: NL2005057C2
Application number: NL2005057A
Authority: NL
Inventors: Jan Noord
Original assignee: Jan Noord
Priority date: 2010-07-08
Filing date: 2010-07-08
Publication date: 2012-01-10
Also published as: CN102374292A; DE102011106920A1; CN102374292B

Description

SEALING ASSEMBLY, DEVICE PROVIDED WITH SUCH ASSEMBLY AND METHOD FOR SEALING

5 The present invention relates to a sealing assembly for sealing a piston or plunger. More specifically, the sealing assembly according to the invention relates to a high pressure seal capable of performing reliable at pressures up to 2000 bar. Such pressures can be encountered when dealing 10 with mixtures of water and oil, for example.

Known seals are often made of polyurethane and are in itself suitable for oil applications. However, when dealing with water or oil-water mixtures in general the performance decreases dramatically, especially at relatively high 15 pressures often to a 2000 bar.

The object of the present invention is to provide a sealing assembly for sealing a piston or plunger with an improved performance as compared to known seals.

This object is achieved with the sealing assembly 20 according to the present invention for sealing a piston or a plunger, the sealing assembly comprising: a seal core that can be placed in a chamber, wherein in use the piston or plunger moves relative to the chamber; 25 - front sealing means; and back sealing means, wherein in use the seal core moves relative to the chamber such that a sealing force is achieved.

The sealing assembly according to the present invention 30 can be used for pistons and plungers, for example. In general a plunger pump consists of a cylinder with a reciprocating plunger in it. The suction and discharge valves are often mounted in the head of this cylinder. In 2 the suction stroke the plunger retracts and the suction valves open such that fluid enters the cylinder. In the forward stroke the plunger pushes this liquid out of the cylinder via the discharge valve.

5 For the purposes of this application for a piston the forces acting on the sealing assembly are reverse as compared to the situation with the plunger.

The sealing assembly according to the invention is provided with a seal core, and front and back sealing means.

10 The seal core can be placed in a chamber of a device like a pump. In use the chamber moves relative to the piston or plunger. According to the invention the seal core, when in use, moves relative to the chamber such that the required sealing force is achieved. That way the sealing force is 15 adapted to the forces acting on the sealing assembly.

For example, in the inlet stroke, as well as in the stationary state, the sealing assembly should be able to hold an under pressure or small vacuum in case the device is fed by a low pressure supply, like a water-tap. The sealing 20 assembly is required to seal against the chamber of the device on one side and against the plunger on the other side. The front sealing means seal between the seal core and the chamber. The back sealing means seal between the core and the plunger.

25 In the displacement or pressure stroke, the sealing assembly is confronted with higher pressures. Again the front sealing means seal between the core and the chamber, and the back sealing means seal between the core and the plunger. The front sealing means are pushed against the seal 30 core and the chamber by the pressure in the cylinder such that the force of the front sealing means is directed outwards, thereby only providing a minimal assistance of sealing the core against the plunger. The sealing force of 3 the core against the plunger is increased with increasing pressure in the cylinder as the sealing assembly is pushed in a direction away from the cylinder volume with the compressed fluid against a support area. This provides the 5 force for sealing the seal core against the plunger.

By automatically increasing the sealing force as function of the pressure in the cylinder, the sealing assembly is capable of operating correctly up to relatively high pressures. For example, it has been shown that the 10 sealing assembly according to the present invention performs correctly when used in an oil-water mixture with pressures of above 10 bar, above 500 bar, above 1000 bar, above 1500 bar, and up to 2000 bar.

Preferably, the front sealing means comprise an O-ring 15 that is provided in a notch of recess of the seal core. Also preferably, the back sealing means comprise an O-ring provided in a groove of the seal core. The seal core is preferably provided in a fluid or a device like a pump. To enable amending the sealing forces the seal core is capable 20 of slightly moving relative to the chamber depending on the forces acting on the sealing assembly in the actual direction of the plunger or piston. Preferably, the front and/or back sealing means comprise nutrile butadiene rubber (NBR) with a hardness of 70 Shore. Preferably, the seal core 25 comprises a polymer material, most preferably ultra high molecular weigth polyethylene (UHMWPE) grade 1000. This specific material is relatively easy to obtain and can be machined with conventional tools, while at the same time is wear resistant and can be applied with water and/or 30 chemicals.

As an additional advantage according to the present invention, the assembly is relatively easy to install. Furthermore, the risks of damaging the seal when installing 4 the sealing means are minimal, thereby increasing the efficiency of the sealing assembly according to the invention.

A further additional advantage of the sealing assembly 5 according to the present invention is that generally available materials can be used without requiring difficult and expensive machining. This results in a cost effective sealing assembly according to the present invention.

In a preferred embodiment according to the present 10 invention the seal core is provided with an opening having a bore, wherein in use the plunger is provided in the opening and wherein the bore is smaller in size than the plunger.

By providing the seal core with a smaller bore as compared to the outside dimensions of the plunger, the 15 material of the seal core is stretched thereby achieving a low pressure sealing effect, and the outside dimensions of the seal core will be increased slightly. Unlike known seals this seal core is not compressed and is only stretched. This enables achieving the required sealing forces.

20 In an illustrative example, a plunger is provided with a diameter of 8 mm. The core bore is provided with a diameter of 7.5 mm. When the plunger is inserted in the core bore, the core is stretched such that a pre-tension is achieved resulting in a low pressure sealing effect. In 25 addition, the stretching allows for wear without the loss of low pressure sealing in the long run. This improves the efficiency of the sealing assembly according to the present invention. The outside diameter of the seal core is slightly smaller then the dimensions of the chamber of the device.

30 For example, the outside diameter of the seal core is 15.76 mm and the bore of the chamber is 16 mm. With the above mentioned dimensions of the plunger and the core bore, the core is stretched and the outside diameter of the core will 5 end up at 16 mm after mounting, thereby exactly matching the dimensions of the chamber. So, in this preferred embodiment the outside dimensions of the seal core are smaller as compared to the dimensions of the chamber of the fluid head.

5 Preferably, the dimensions of the plunger, the chamber, the core bore and the seal core outside dimensions are matched such that the seal core meets the chamber dimensions after mounting the plunger in the core. This preferably stretches the material of the seal core when in use.

10 Preferably, the dimensions of the seal core, before and after mounting the plunger and the sealing assembly in the chamber, are related as follows:

Area final outside diameter of the core - final inside 15 diameter of the core = area outside diameter before mounting - inside diameter before mounting.

In the above example the outside diameter before mounting is 15.76 mm and the inside diameter is 7.5 mm.

20 After mounting the inside diameter is 8 mm and the outside diameter of the core is 16 mm. In this example the outside dimensions of the seal core before mounting are smaller than the size of the chamber. This enables stretching the core material.

25 In an alternative preferred embodiment according to the present invention the outside dimensions of the seal core are larger than the size of the chamber, and the size of the bore is larger than the size of the plunger or piston.

By providing a seal core that is larger than the 30 chamber and a bore that is also larger than the size of the plunger or piston, the above principle of sealing is reversed such that in accordance with the wordings used in this application, the seal assembly can be used as a piston 6 seal. The dimensions are related to each other in a similar way as mentioned above.

In a preferred embodiment according to the present invention in use the back sealing means seal against the 5 support area of a body.

By sealing against a support area of a body, the sealing force is increased when confronted with an increased pressure inside the cylinder. Preferably, the body is a gland or the like. Preferably, the back sealing means is 10 provided in a groove of the seal core. Also preferably, this groove is constructed such that it nearly accommodates a fully compressed back sealing means like an O-ring. When the cylinder volume is pressurized the full frontal area of the sealing assembly is confronted with a force. The counter 15 force is provided by the compressed back sealing means supporting the sealing assembly against the body. As the support area of the back sealing means against the body is smaller than the frontal area of the sealing assembly, the pressure generated in the groove of the seal core is higher 20 as compared to the frontal pressure acting on the sealing assembly. This results in a sealing force that is larger than the engaged frontal force thereby creating a tight seal that is adapted to the forces of the sealing assembly. A high force is countered by a slightly higher counter force, 25 while a relatively small force is countered by a little higher counter force. This reduces wear of the sealing assembly according to the present invention.

The present invention also relates to a device provided with a sealing assembly as mentioned above.

30 Such device provides the same effects and advantages as those related to the sealing assembly. For example, such device is a piston pump, plunger pump or an engine.

7

The present invention further also relates to a method for sealing comprising the steps of providing a sealing assembly as mentioned above.

Such method provides the same effects and advantages as 5 those related to the sealing assembly.

Further advantages, features and details of the invention are elucidated on basis of preferred embodiments thereof wherein reference is made to the accompanying drawings, wherein: 10 - Figure 1 shows a plunger seal of a high pressure pump according to the invention;

Figure 2 shows the seal core of figure 1;

Figure 3A and B show the seal assembly of figure 1; 15 - Figure 4A and B show the seal assembly in the suction stroke and pressure stroke, respectively; and

Figure 5 shows an alternative embodiment of the seal assembly according to the invention.

20 Seal assembly 2 (figure 1) can be used in a high pressure pump 4. Pump 4 comprises a fluid head 6, a seal support disc 8, and a gland 10. In addition, pump 4 is provided with an inlet 12 and an inlet check valve 14, as well as an outlet 16 and an outlet check valve 18. Plunger

25 20 can be moved along its axial direction in a direction A

corresponding to the suction stroke, and in a direction B corresponding to the displacement or pressure stroke. Seal assembly 2 comprises a core 22 that is placed in chamber 23 of pump 4, a front O-ring 24, and a back O-ring 26. In the 30 illustrated embodiment O-rings 22, 24 are made of NBR with a harness of 70 Shore. Seal core 22 is cut on a standard lathe with simple sharp cutters. The base material for a seal core 22 is UHMWPE with a grade of 1000.

8

Core 22 (figure 2) has a bore 28 for plunger 20, a recess 30 for O-ring 24, and groove 32 for O-ring 26. In the illustrated embodiment bore 28 has a diameter of 7.5 mm, groove 32 has for its centre line a diameter of 11.5 mm with 5 a depth of groove 32 into core 22 of 1.5 mm and a maximum width of groove 32 of 2 mm. The length of core 22 in its axial direction is 6.5 mm and for recess 30 2.5 mm. The outside diameter of core 22 is 15.76 mm and the outside diameter of recess 30 is 12.4 mm.

10 Seal assembly 2 comprises core 22 and O-rings 24, 26 (figure 3 A and B) that are put together. In the illustrated embodiment the plunger diameter is 8 mm and the recess or chamber in the fluid head 6 of pump 4 that is provided for sealing assembly 2 has a diameter of 16 mm. For the given 15 dimensions the surface area of core 22 before mounting plunger 20 is 150.8 mm2 such that after assembly core 22 is stretched with an inner diameter of 8 mm and an outside diameter of 16 mm just fitting in chamber 23 provided in fluid head 6.

20 In plunger pump 4, when in the suction stroke or in rest, seal assembly 2 engages surface area 34 of fluid head 6. Front O-ring 24 seals core 22 against fluid head 6 along surface area 36. Back O-ring 26 slightly contacts surface area 38 of seal support disc 8 and seals core 22 against 25 surface area 40 of plunger 20. During the inlet or suction stroke or when in rest (figure 4A) seal assembly 2 maintains an under pressure in pump 4. This is achieved by sealing against surface 36 by O-ring 24, and sealing against surface 40 with the stretching elasticity of core 22.

30 In a displacement or pressure stroke (figure 4B) a force is acting on surface 34. Core 22 is pushed in the axial direction of plunger 20 backwards seen from the cylinder. The sealing between core 22 and fluid head 6 is 9 achieved by O-ring 24 on surface 36. As core 22 is pushed backwards O-ring 26 is pushed or compressed in groove 32 by surface area 38. Groove 32 is constructed such that it nearly accommodates the fully compressed O-ring 26. As 5 surface area 38 is smaller than surface area 34 the pressure generated in groove 32 of core 22 is larger as compared to the frontal pressure against surface area 34. This results in a sealing force acting on surface area 40 on plunger 20 such that a tight seal is achieved. This is illustrated by 10 force profile 42 (figure 4B) in the displacement or pressure stroke as compared to the force profile 44 in the suction stroke or rest position (figure 4A). This achieves a sealing force that is related to the applied pressure on the inside of pump 4. This automatic adapting of the applied sealing 15 forces reduces wear to a minimum. In addition, in the illustrated embodiment, standard material is used. Experiments have shown that the seal assembly operates correctly for pressures up to 2000 bar.

In an alternative embodiment 46 a seal core 48 (figure 20 5) is provided. Seal core 48 is provided with a front O-ring 50 and a back O-ring 52. As mentioned before, in piston embodiment 46 core 48 is sealed to piston 54 using O-ring 50 that is provided on the piston side of core 48. For the back O-ring 52 the functioning is similar as described above.

25 It will be understood that the dimensions given in the above examples are for illustrative purposes and that other dimensions can be used in a similar way. This also applies to the type of materials that are used.

The present invention is by no means limited to the 30 above described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

10

Clauses 1. Sealing assembly, for sealing a piston or a plunger, 5 comprising: - a seal core that can be placed in a chamber, wherein in use the piston or plunger moves relative to the chamber; - front sealing means; and 10 - back sealing means, wherein in use the seal core moves relative to the chamber such that a sealing force is achieved.

2. Sealing assembly according to clause 1, wherein the 15 seal core is provided in a chamber of a fluid head.

3. Sealing assembly according to clause 1 or 2, wherein the sealing core comprises a polymer material, preferably ultra high molecular weight polyethylene.

20 4. Sealing assembly according to clause 1, 2 or 3, wherein the seal core is provided with an opening having a bore, wherein in use a plunger is provided in the opening, and wherein the bore is smaller than the size 25 of the plunger or piston.

5. Sealing assembly according to any of clauses 1-4, wherein the outside dimensions of the seal core are smaller than the size of the chamber.

11 6. Sealing assembly according to any of clauses 1-4, wherein the outside dimensions of the seal core are larger than the size of the chamber, and the bore is larger than the size of the plunger or piston.

5 7. Sealing assembly according to any of clauses 1-6, wherein in use the material of the seal core is stressed.

10 8. Sealing assembly according to any of the clauses 1-7, wherein in use the back sealing means seal against a support area of a body.

9. Sealing assembly according to clause 8, wherein in use 15 front and back sealing means are provided in a groove of the seal core with the groove slightly smaller as the compressed back sealing means.

10. Sealing assembly according to clause 8 or 9, wherein 20 the support area is smaller than the frontal area of the seal core.

11. Device provided with a sealing assembly according to any of the clauses 1-10.

25 12. Method for sealing, comprising the step of providing a sealing assembly according to any of clauses 1-10.

Claims

A sealing assembly for sealing a piston or a plunger, comprising: 5. a sealing core positionable in a chamber in which, in use, the piston or plunger moves relative to the chamber; - front sealants; and - rear sealing means, wherein the sealing core, in use, moves relative to the chamber such that a sealing force is achieved.

2. Sealing assembly according to claim 1, wherein the sealing core is provided in a chamber of a fluid head.

3. Sealing assembly according to claim 1 or 2, wherein the sealing core comprises a polymeric material, preferably UHMWP.

4. Sealing assembly according to claim 1, 2 or 3, wherein the sealing core is provided with an opening with a bore in which a plunger is provided in use, and in which the bore is smaller than the size of the plunger or piston.

5. Sealing assembly according to one or more of claims 1-4, wherein the outer dimensions of the sealing core are smaller than the size of the chamber.

6. Sealing assembly according to one or more of claims 1-4, wherein the outer dimensions of the sealing core are smaller than the size of the chamber, and wherein the bore is larger than the size of the plunger or piston.

A sealing assembly according to one or more of claims 1-6, wherein in use the material of the sealing core is stretched. 10

Sealing assembly according to one or more of claims 1-7, wherein in use the rear sealing means seal against a supporting surface of a body. 15

9. Sealing assembly as claimed in claim 8, wherein in use the rear sealing means are provided in a groove of the sealing core, the groove being somewhat smaller than the compressed rear sealing means.

A sealing assembly according to claim 8 or 9, wherein the supporting surface is smaller than the frontal surface of the sealing core. 25

Device provided with a sealing assembly according to one or more of claims 1-10.

12. Method for sealing, comprising the step of providing a sealing assembly according to one or more of claims 1-10.