GB2142413A - Plunger construction for pump - Google Patents

Abstract

A plunger for a plunger pump, being a composite, reciprocable mechanical component, wherein two members (10, 11) with a gap between them but also in axial contact (12) are joined by an elastomeric bonding material (13) disposed in the gap, whereby forces can be transmitted from one member to the other in one direction through said axial contact and in the opposite direction through the bonding material. Alternative configurations are illustrated in Figs. D and E (not shown). <IMAGE>

Description

SPECIFICATION Plunger The invention relates to composite, reciprocable mechanical components, particularly to composite plungers for plunger pumps.

The type of pump that is relevant to the invention is a pump having a reciprocating plunger or piston moving inside a stationary cylinder and carried by a metal cross-head. There is normally a stationary seal located in the cylinder which bears on the outside cylindrical surface of the plunger. On the withdrawal stroke water, or other fluid, is drawn into the cylinder, and on the power stroke the fluid is displaced by the plunger at pressures as high as 1500 bars, though the majority of pumps work at around 250 bars or less.

The plunger is often made of ceramic materials (frequently alumina), since these materials not only withstand the compressive mechanical forces applied to them during the power stroke very well, but also are corrosion resistant, and give a good life to the normally elastomeric seals on which they rub, through the special nature of their surface finish.

There is always a problem of fixing the ceramic plunger to the cross-head in such a way that a) The ceramic plunger and the cross-head are coaxial within fine limits (if they are not then poor sealing and possible breakage of the ceramic will occur in service).

b) There is no appreciable tensile stress applied to the ceramic.

c) There is no possible secondary leak path such that the high pressure water or other fluid pumped can contaminate the oil on the cross-head side of the assembly, or build up an internal pressure inside a hollow ceramic plunger and thus give rise to bursting forces, or simply reduce the efficiency of the pump by allowing leakage.

Sketches A and B of the accompanying drawings show typical arrangements that are commonly used at present. The arrangement shown in sketch A is an expensive arrangement to make because the inter nal diameter locating areas and both ends 2,3 of the ceramic 4 have to be ground to fit the plunger mandrel 5. Also a secondary leakpath exists around the fixing nut 6 at the high pressure end. If the gap between the steel mandrel and the ceramic is tightly sealed, then there is the risk of breakage of the ceramic due to differential thermal expansion.

The arrangement of mandrel 7 and ceramic 8 shown in sketch B is also expensive, because it is normally necessary to finish the grinding of the ceramic external diameter after the glue filler 9 has set. Any misalignment of parts in this design will give rise to forces which may damage the glue bond and ultimately break the ceramic (axial force on the ceramic on the pressure stroke can be as high as 10 tons).

The aim of the invention is to improve on these prior plungers and give an efficient and economically produced design.

To this end the invention provides a composite, reciprocable mechanical compnent, particularly a plunger for a plunger pump, wherein two members with a gap betweem then but also in axial contact are joined by an elastomeric bonding material disposed in the gap, whereby forces can be transmitted from one member to the other in one direction through said axial contact and in the opposite direction through the bonding material.

In particular, in a plunger, one member may be a ceramic plunger head and the other a metal mandrel by means of which the plunger is reciprocated.

Thus in particularthe idea isto use a polymeric type material which is preferably vulcanised to provide a flexible elastic joint between the ceramic plunger and the mandrel. Such a construction will better withstand shock and vibration which would otherwise be likely to cause damage. Preferably, the polymeric material is chemically bonded to one or both of the components to prevent their separation or relative movement.

Further advantages of the invention, at least in its preferred forms described below are that: 1) the ceramic part can be made more economically as less expensive grinding proceeses are required; 2) the need for grinding after assembly is eliminated; 3) because the bond is flexible it is able to accommodate thermal expansion differences between the ceramic plunger and the steel mandrel that otherwise might lead to damage; 4) the flexible nature of the joint between the parts will tend to accommodate minor misalignments better than a rigid joint such as commonly used at present.

It may be noted that in all cases there can be ceramic - metal contact at the point at which the axial force is to be transmitted. The polymer only has to be strong enough to withstand the low suction, friction and inertia forces during the induction stroke.

In the accompanying drawings sketches C, D, E illustrate the invention, a steel mandrel being referenced 10 and an alumina ceramic plunger 11 in each case. The mandrels and plungers are in axial contact at 12, and gaps between them are filled with injection moulded rubber 13. The simplicity of the designs may be noted, particularly in sketch E. The design of sketch D is the same as that of sketch B except for the addition of a passage 14 for the injection moulding of the rubber, which passage need not necessarily be in the position shown. Parts are held in accurate register in the injection moulding tool, and so can be made to finished size before assembly.

1. A plunger for a plunger pump, being a composite, reciprocable mechanical component, wherein two members with a gap between them but also in axial contact are joined by an elastomeric bonding material disposed in the gap, whereby forces can be transmitted from one member to the other in one direction through said axial contact and in the opposite direction through the bonding material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Plunger The invention relates to composite, reciprocable mechanical components, particularly to composite plungers for plunger pumps. The type of pump that is relevant to the invention is a pump having a reciprocating plunger or piston moving inside a stationary cylinder and carried by a metal cross-head. There is normally a stationary seal located in the cylinder which bears on the outside cylindrical surface of the plunger. On the withdrawal stroke water, or other fluid, is drawn into the cylinder, and on the power stroke the fluid is displaced by the plunger at pressures as high as 1500 bars, though the majority of pumps work at around 250 bars or less. The plunger is often made of ceramic materials (frequently alumina), since these materials not only withstand the compressive mechanical forces applied to them during the power stroke very well, but also are corrosion resistant, and give a good life to the normally elastomeric seals on which they rub, through the special nature of their surface finish. There is always a problem of fixing the ceramic plunger to the cross-head in such a way that a) The ceramic plunger and the cross-head are coaxial within fine limits (if they are not then poor sealing and possible breakage of the ceramic will occur in service). b) There is no appreciable tensile stress applied to the ceramic. c) There is no possible secondary leak path such that the high pressure water or other fluid pumped can contaminate the oil on the cross-head side of the assembly, or build up an internal pressure inside a hollow ceramic plunger and thus give rise to bursting forces, or simply reduce the efficiency of the pump by allowing leakage. Sketches A and B of the accompanying drawings show typical arrangements that are commonly used at present. The arrangement shown in sketch A is an expensive arrangement to make because the inter nal diameter locating areas and both ends 2,3 of the ceramic 4 have to be ground to fit the plunger mandrel 5. Also a secondary leakpath exists around the fixing nut 6 at the high pressure end. If the gap between the steel mandrel and the ceramic is tightly sealed, then there is the risk of breakage of the ceramic due to differential thermal expansion. The arrangement of mandrel 7 and ceramic 8 shown in sketch B is also expensive, because it is normally necessary to finish the grinding of the ceramic external diameter after the glue filler 9 has set. Any misalignment of parts in this design will give rise to forces which may damage the glue bond and ultimately break the ceramic (axial force on the ceramic on the pressure stroke can be as high as 10 tons). The aim of the invention is to improve on these prior plungers and give an efficient and economically produced design. To this end the invention provides a composite, reciprocable mechanical compnent, particularly a plunger for a plunger pump, wherein two members with a gap betweem then but also in axial contact are joined by an elastomeric bonding material disposed in the gap, whereby forces can be transmitted from one member to the other in one direction through said axial contact and in the opposite direction through the bonding material. In particular, in a plunger, one member may be a ceramic plunger head and the other a metal mandrel by means of which the plunger is reciprocated. Thus in particularthe idea isto use a polymeric type material which is preferably vulcanised to provide a flexible elastic joint between the ceramic plunger and the mandrel. Such a construction will better withstand shock and vibration which would otherwise be likely to cause damage. Preferably, the polymeric material is chemically bonded to one or both of the components to prevent their separation or relative movement. Further advantages of the invention, at least in its preferred forms described below are that: 1) the ceramic part can be made more economically as less expensive grinding proceeses are required; 2) the need for grinding after assembly is eliminated; 3) because the bond is flexible it is able to accommodate thermal expansion differences between the ceramic plunger and the steel mandrel that otherwise might lead to damage; 4) the flexible nature of the joint between the parts will tend to accommodate minor misalignments better than a rigid joint such as commonly used at present. It may be noted that in all cases there can be ceramic - metal contact at the point at which the axial force is to be transmitted. The polymer only has to be strong enough to withstand the low suction, friction and inertia forces during the induction stroke. In the accompanying drawings sketches C, D, E illustrate the invention, a steel mandrel being referenced 10 and an alumina ceramic plunger 11 in each case. The mandrels and plungers are in axial contact at 12, and gaps between them are filled with injection moulded rubber 13. The simplicity of the designs may be noted, particularly in sketch E. The design of sketch D is the same as that of sketch B except for the addition of a passage 14 for the injection moulding of the rubber, which passage need not necessarily be in the position shown. Parts are held in accurate register in the injection moulding tool, and so can be made to finished size before assembly. CLAIMS

1. A plunger for a plunger pump, being a composite, reciprocable mechanical component, wherein two members with a gap between them but also in axial contact are joined by an elastomeric bonding material disposed in the gap, whereby forces can be transmitted from one member to the other in one direction through said axial contact and in the opposite direction through the bonding material.

2. A plunger as claimed in Claim 1 and substantially as described with reference to or as shown by sketches C, D and E of the Drawings.