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EP-4737725-A1 - PISTON MEMBRANE PUMP FOR PUMPING A LIQUID

EP4737725A1EP 4737725 A1EP4737725 A1EP 4737725A1EP-4737725-A1

Abstract

A piston membrane pump (100) for pumping a liquid, comprising: housing (101) with a chamber (106) having an inlet (107) and outlet (108); a piston (102) in the housing, reciprocating along a longitudinal axis (111) to pump liquid by changing the chamber's volume; a membrane element (103a) sealing the piston (102) to the housing (101); and an actuator (104) driving the piston (102) between a rear (R1) and front end position (F1); and a control unit (105) configured to: control the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) for the piston along the longitudinal axis, wherein each set of end positions comprises a rear end position (R1-Rn) and a front end position (F1-Fn) where the distance (L) between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length (L) of the piston.

Inventors

  • NORDQVIST, CHRISTER
  • LINDE, CHRISTIAN

Assignees

  • Tetra Laval Holdings & Finance S.A.

Dates

Publication Date
20260506
Application Date
20251022

Claims (15)

  1. A piston membrane pump (100) for pumping a liquid, the piston membrane pump (100) comprising: a housing (101) defining a chamber (106), the chamber (106) having an inlet (107) and an outlet (108) for the liquid; a piston (102) arranged within the housing (101) and configured to reciprocate along a longitudinal axis (111) to pump the liquid through the inlet (107) and the outlet (108) by repeatedly decreasing and increasing the volume of the chamber (106); a membrane element (103a) connected to both the piston (102) and the housing (101), forming a seal between the piston (102) and the housing (101); an actuator (104) operatively connected to the piston (102) to drive the reciprocating motion of the piston (102) between a rear end position (R1) and a front end position (F1) along the longitudinal axis (111); characterized by a control unit (105) configured to: - control the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) for the piston (102) along the longitudinal axis (111), wherein each set of end positions comprises a rear end position (R1 - Rn) and a front end position (F1 - Fn) where the distance (L) between the rear end position (R1 - Rn) and the front end position (F1 - Fn) of each set corresponds to a predetermined, full stroke length (L) of the piston (102).
  2. The piston membrane pump (100) according to claim 1, wherein the different points in time are determined by predetermined time intervals and/or receiving a signal indicative of an interruption in an operational cycle of the piston membrane pump (100).
  3. The piston membrane pump (100) according to any preceding claim, wherein the multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) differ from each other by their respective set of end positions (R1,F1; R2,F2; Rn,Fn) shifted by an offset distance value (Δx) along the longitudinal axis (111).
  4. The piston membrane pump (100) according to claim 3, wherein the offset distance value (Δx) is in the range of 2 mm to 10 mm.
  5. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: record a value representing the number of reciprocating motions the actuator (104) drives the piston (102) at each of the respective different sets of end positions (R1,F1; R2,F2; Rn,Fn).
  6. The piston membrane pump (100) according to claim 5, wherein the control unit (105) is configured to: distribute the number of reciprocating motions evenly across the multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn).
  7. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: set the piston (102) in a reset position, defined by an abutment surface (133) of the housing (101) that prevents further movement of the piston (102) in one direction of the longitudinal axis (111), before controlling the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of said multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn).
  8. The piston membrane pump (100) according to any preceding claim, wherein the membrane element (103a) comprises, between its connection points (114a, 116) to the housing (101) and the piston (102), a 180-degree fold (115a) that moves along a length (L2) of the membrane element (103a) when the piston (102) reciprocates between the rear end position (R1) and the front end position (F1).
  9. The piston membrane pump (100) according to any preceding claim, wherein the membrane element (103a) is connected to a first end (102a) of the piston (102), and wherein the piston membrane pump (100) further comprises: a further membrane element (103b) connected to both the piston (102) and the housing (101), at a second end (102b) of the piston (102) opposite the first end (102a), forming an additional seal between the piston (102) and the housing (101), such that a sealed space (119) is formed between the housing (101), the piston (102) and the membrane elements (103a, 103b); and a vacuum connection (121) leading to the sealed space (119).
  10. The piston membrane pump (100) according to claim 9, wherein the housing (101) comprises: a first end section (101a) that comprises the inlet (107) and the outlet (108); a second end section (101b) configured to accommodate a coupling arrangement (118) to couple the piston (102) to the actuator (104); and an intermediate section (101c) connected to both end sections (101a-b), thereby forming a hollow space (112) that accommodates the piston (102), wherein the membrane element (103a) is attached to the housing (101) via a flange (114a) located at the connection between the first end section (101a) and the intermediate section (101b); and the further membrane element (103b) is attached to the housing (101) via a flange (114b) located at the connection between the second end section (101b) and the intermediate section (101c).
  11. The piston membrane pump (100) according to any preceding claim, wherein the inlet (111) is arranged to cooperate with an inlet valve (123), and the outlet (112) is arranged to cooperate with an outlet valve (124), such that liquid is pumped through the housing (101) when the actuator (104) drives the piston (102).
  12. The piston membrane pump (100) according to claim 11, wherein the control unit (105) is configured to: transmit a control signal to the inlet valve (123) to set it in an open state when the actuator (104) is controlled to switch between the different sets of end positions (R1,F1; R2,F2; Rn,Fn) used to drive the piston (102).
  13. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: control the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of said multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) such that the rear and front end positions first monotonically increase over time and then monotonically decrease over time.
  14. A filling machine (200) for filling liquid product (201) in packages (202), wherein the liquid is dispensed by pumping with a piston membrane pump (100) according to any preceding claim.
  15. A method of controlling a piston membrane pump (100), the piston membrane pump (100) comprising: a housing (101) defining a chamber (106) with an inlet (107) and an outlet (108) for the liquid; a piston (102) configured to reciprocate along a longitudinal axis (111) to pump the liquid by changing the volume of the chamber (106); a membrane element (103a) forming a seal between the piston (102) and the housing (101); and an actuator (104) operatively connected to the piston (102) to drive its reciprocating motion, the method comprising: - controlling (S1) the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) for the piston (102) along the longitudinal axis (111), wherein each set of end positions (R1,F1; R2,F2; Rn,Fn) comprises a rear end position (R1 - Rn) and a front end position (F1 - Fn) where the distance (L) between the rear end position (R1 - Rn) and the front end position (F1 - Fn) of each set corresponds to a predetermined, full stroke length (L) of the piston (102).

Description

Technical Field The invention relates to a piston membrane pump for pumping a liquid. The invention also relates to a filling machine, and to method of controlling a piston membrane pump. Background A known piston membrane pump for pumping a liquid comprises a housing defining a chamber. The chamber has an inlet and an outlet for the liquid. The known piston membrane pump further comprises a piston arranged within the housing. The piston is configured to reciprocate along a longitudinal axis to pump the liquid through the inlet and the outlet by repeatedly decreasing and increasing the volume of the chamber. The known piston membrane pump further comprises a membrane element connected to both the piston and the housing. The membrane element forms a seal between the piston and the housing. The known piston membrane pump further comprises an actuator operatively connected to the piston to drive the reciprocating motion of the piston between a rear end position and a front end position along the longitudinal axis. Summary In the piston membrane pump, after start-up, the actuator drives the reciprocating motion of the piston between the same rear end position and the same front end position along the longitudinal axis throughout operation of the pump. It has been found that this may cause stress on the regions of the membrane element that "bend" or turn" when the piston is in the end positions, as will be explained in detail further on. This stress can eventually lead to a rupture of the membrane element. Every time a rupture occurs, for example, in a filling machine that comprises the piston membrane pump, the machine needs to be cleaned and sterilized, which can take a significant amount of time. It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the piston membrane pump. In particular, it is an object to achieve fewer ruptures of the membrane element of the piston membrane pump. To solve these objects, according to a first aspect, a piston membrane pump for pumping a liquid is provided. The piston membrane pump comprises a housing defining a chamber, the chamber having an inlet and an outlet for the liquid; a piston arranged within the housing and configured to reciprocate along a longitudinal axis to pump the liquid through the inlet and the outlet by repeatedly decreasing and increasing the volume of the chamber; a membrane element connected to both the piston and the housing, forming a seal between the piston and the housing; an actuator operatively connected to the piston to drive the reciprocating motion of the piston between a rear end position and a front end position along the longitudinal axis; and a control unit configured to: control the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions for the piston along the longitudinal axis, wherein each set of end positions comprises a rear end position and a front end position where the distance between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston. For the multiple, different sets of end positions, the distance between the rear end position and the front end position (the full stroke length) may thus be the same for each set in the different sets. It may be said that each set of end positions comprises a rear end position and a front end position where the distance between the rear end position and the front end position of each set corresponds to the same, predetermined, full stroke length of the piston. It may also be said that each set of end positions may define the same predetermined full stroke length, even though the rear and front end positions in the respective set vary along the longitudinal axis. By controlling the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions for the piston along the longitudinal axis, the stress on the membrane element is not always applied to the same region of the membrane element throughout operation of the piston membrane pump, which in turn will make the membrane element less prone to ruptures. In other words, stress fractures on the membrane element may be decreased, and/or the lifetime of the membrane element may be extended. Moreover, since the distance between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston, the filling volume of the liquid may remain constant regardless of which set is used. In further detail, it has been observed that the operational lifetime of the membrane is significantly extended by using the described piston membrane pump. Specifically, because the membrane is connected to the piston, it follows the reciprocating motion of the piston as it moves between the rear end and front end positio