I am trying to understand the effects of prolonged exposure to high temperatures on the coils of solenoid valves, vibrational pumps and similar devices, and whether the negative effects are reversible.
Most medium sized espresso machines have a variety of solenoid valves for regulating flow of water/coffee, and a vibrational pump usually manufactured by Ulka, usually the EP5. The Ulka - which has a modular construction - has a coil similar to that of a solenoid valve (such as those manufactured by Parker/Lucifer), which moves a steel piston to and fro against a spring to pump water. Between the coil and the plastic tube containing the steel piston there is an iron sleeve (magnetically contiguous with an iron path in a loop around the coil) around 2 to 2.5 mm thick which appears to play a crucial role in the concentration of the induced magnetic field from the coil on the steel piston. The Ulka is particularly interesting because of its modular construction, so that parts can be freely interchanged between different pumps.
After a number of years' use these devices have reduced and/or erratic performance, as a result of prolonged exposure to quite high temperatures. Because of the modular construction, when they fail functioning parts are often interchanged between various old units to make one good unit. I have observed that the maximum pressure that a used Ulka pump can develop varies substantially, and depends essentially on the coil/iron sleeve combination rather than the piston construction, which (if it is visually in good condition) has no effect on the maximum pressure. What is interesting to me is that of the coil/iron sleeve combination, it is the iron sleeve which is crucial rather than the coil itself - I think actually the coil itself has zero effect, although I would not state that categorically. Supposing I have two pumps which in good physical condition and both of which vibrate when current is applied, where Pump A is able to develop 15 bars of pressure, while Pump B (or the same model EP5) develops only 4 bars. Consider the effect of swapping individual components between Pump A and Pump B, and the result on performance of the two pumps. Swapping piston construction (or individual components of the piston construction) has no effect on performance. If I swap the coil/iron sleeve combination, then the performance of the two pumps is reversed: Pump A 4 bars, pump B 15 bars. Interestingly, if I keep the coil itself unchanged and swap only the iron sleeve construction*, the pressure developed is fairly close to or equal to Pump A 4 bars and Pump B 15 bars (from memory, I cannot remember whether all the difference is in the sleeve or only most of it). * EDIT: It is actually not just the sleeve over the piston construction, but also an iron frame that forms a magnetic loop around the coil, and this frame has to be dismantled to remove the iron sleeve; my detailed experiments were some years ago, and I think I also tried swapping the sleeve/frame part-by-part, but cannot remember the results, although I think I am right in saying the inner sleeve is the most critical component which changes in performance.
Here is my question. As far as I can tell, none of the components in the Ulka pump (piston, iron sleeve, iron frame, coil) exhibits any permanent magnetism at all. So (1) what is the nature of the change in the iron as a result of exposure to heat*, resulting in reduced performance? (* There is a little bit of extrapolation involved here, as I don't have definitive evidence that the deterioration in Ulka performance is the result of heat rather than cumulative electromagnetic use; the extrapolation is from my experience of the Parker/Lucifer solenoid valves (such as part no. E121C13 2-way valve and coil part no. 483510, https://parcom.de/kataloge/Parker_Lucifer_Part-IV.pdf page 342) - in this case it seems pretty clear that the deterioration is directly related to heat exposure; with the Parker/Lucifer swapping the coil/magnetic path combination has the same effect as the Ulka, but it is an integrated unit so swapping the magnetic path alone is not possible). And (2) whatever the change in the iron magnetic path is, can that change be reversed? I think this is the main failure mode of the solenoid valve in espresso machines rather than the coil burning out.
(Just thinking about that magnetic path through the iron sleeve and frame for a moment: if my memory of magnetism from some half a century ago is not too far out, there should be a magnetic field induced by the coil of which the most concentrated part would go through the iron magnetic path and presumably also the steel piston; what the relationship is between the magnetic path through the iron and the magnetic path through the steel piston is not completely clear to me, nor the apparent lack of a heat exposure problem on the steel piston - could that have something to do with the speed of build-up/collapse of the magnetic field in iron as opposed to steel?)
Most medium sized espresso machines have a variety of solenoid valves for regulating flow of water/coffee, and a vibrational pump usually manufactured by Ulka, usually the EP5. The Ulka - which has a modular construction - has a coil similar to that of a solenoid valve (such as those manufactured by Parker/Lucifer), which moves a steel piston to and fro against a spring to pump water. Between the coil and the plastic tube containing the steel piston there is an iron sleeve (magnetically contiguous with an iron path in a loop around the coil) around 2 to 2.5 mm thick which appears to play a crucial role in the concentration of the induced magnetic field from the coil on the steel piston. The Ulka is particularly interesting because of its modular construction, so that parts can be freely interchanged between different pumps.
After a number of years' use these devices have reduced and/or erratic performance, as a result of prolonged exposure to quite high temperatures. Because of the modular construction, when they fail functioning parts are often interchanged between various old units to make one good unit. I have observed that the maximum pressure that a used Ulka pump can develop varies substantially, and depends essentially on the coil/iron sleeve combination rather than the piston construction, which (if it is visually in good condition) has no effect on the maximum pressure. What is interesting to me is that of the coil/iron sleeve combination, it is the iron sleeve which is crucial rather than the coil itself - I think actually the coil itself has zero effect, although I would not state that categorically. Supposing I have two pumps which in good physical condition and both of which vibrate when current is applied, where Pump A is able to develop 15 bars of pressure, while Pump B (or the same model EP5) develops only 4 bars. Consider the effect of swapping individual components between Pump A and Pump B, and the result on performance of the two pumps. Swapping piston construction (or individual components of the piston construction) has no effect on performance. If I swap the coil/iron sleeve combination, then the performance of the two pumps is reversed: Pump A 4 bars, pump B 15 bars. Interestingly, if I keep the coil itself unchanged and swap only the iron sleeve construction*, the pressure developed is fairly close to or equal to Pump A 4 bars and Pump B 15 bars (from memory, I cannot remember whether all the difference is in the sleeve or only most of it). * EDIT: It is actually not just the sleeve over the piston construction, but also an iron frame that forms a magnetic loop around the coil, and this frame has to be dismantled to remove the iron sleeve; my detailed experiments were some years ago, and I think I also tried swapping the sleeve/frame part-by-part, but cannot remember the results, although I think I am right in saying the inner sleeve is the most critical component which changes in performance.
Here is my question. As far as I can tell, none of the components in the Ulka pump (piston, iron sleeve, iron frame, coil) exhibits any permanent magnetism at all. So (1) what is the nature of the change in the iron as a result of exposure to heat*, resulting in reduced performance? (* There is a little bit of extrapolation involved here, as I don't have definitive evidence that the deterioration in Ulka performance is the result of heat rather than cumulative electromagnetic use; the extrapolation is from my experience of the Parker/Lucifer solenoid valves (such as part no. E121C13 2-way valve and coil part no. 483510, https://parcom.de/kataloge/Parker_Lucifer_Part-IV.pdf page 342) - in this case it seems pretty clear that the deterioration is directly related to heat exposure; with the Parker/Lucifer swapping the coil/magnetic path combination has the same effect as the Ulka, but it is an integrated unit so swapping the magnetic path alone is not possible). And (2) whatever the change in the iron magnetic path is, can that change be reversed? I think this is the main failure mode of the solenoid valve in espresso machines rather than the coil burning out.
(Just thinking about that magnetic path through the iron sleeve and frame for a moment: if my memory of magnetism from some half a century ago is not too far out, there should be a magnetic field induced by the coil of which the most concentrated part would go through the iron magnetic path and presumably also the steel piston; what the relationship is between the magnetic path through the iron and the magnetic path through the steel piston is not completely clear to me, nor the apparent lack of a heat exposure problem on the steel piston - could that have something to do with the speed of build-up/collapse of the magnetic field in iron as opposed to steel?)