ChillerTheatre
Mechanical
- Feb 9, 2006
- 2
Does anyone know of any reliability problems with pressure powered condensate pumps causing the springs to break or mechanisms to habitually jam up?
I am working on the design of a steam distribution and condensate return system. In the design, I would like to use gravity fed condensate tanks with pressure powered pumps returning the condensate to an over head pipe system.
Some people I am working with began to say that they had "had problems" with these and don't like to use them. I don't like these vague "problems", especially when I am being told an entire class of equipment is off limits for use. Yes, the equipment needs to be appropriately applied in order for it to work properly, but unless the concept is flawed I should still be allowed to apply it (properly).
I pressed the issue and was told that there were problems with these pumps failing continuously on a job and some consultant had analyzed the situation and found that the pump steam motive pressure was too high even though the pumps were rated to handle well over the applied pressure. I was further told that reducing the pressure eliminated the repeat failures. But I still was not told what the actual failures were.
I figured that if these pumps as a class of equipment were failing in droves due to "high pressure" I would find some documentation about this plague somewhere. I have not found such documentation. I asked the Spirax-Sarco representative if he had heard of these failure problems and he said he had not (I would expect that if some of his competitors equipment to have trouble, he would say so).
I later heard but have seen no evidence that the pumps in question were failing due to the springs breaking. This would be a low cycle failure mechanism since they were supposedly lasting only a month. The other problem I heard was that these pumps tended to stick, allowing the condensate to flood back into the steam spaces.
The particular brand of pump failing I found out was a Watson-McDaniel. It appears to me that the springs are of Inconel X-750 for corrosion resistance and are in compression. I do not see how pressure directly affects the spring cycle stresses since the pressure does not change the compression or stroke distance.
I suppose higher motive pressure would cause the fluid to be expelled faster and the toggle mechanism to snap faster and harder. This could cause spring resonance ringing every time it was snapped with possible failures at stress concentrations I suppose. The only other thing that would change would be the condensate temperature. The units are rated for 150 psig, meaning the condensate temperature would be a maximum of 366F. I don't think the pressure being used was that high. But I still think I would see some industrial reliability data or conplaints somewhere.
I am tending to think either these were dud pumps and the customer did not have the patience to find out why they were failing, or these problems started after poor maintenance, possibly using springs that were not Inconel x-750.
I am working on the design of a steam distribution and condensate return system. In the design, I would like to use gravity fed condensate tanks with pressure powered pumps returning the condensate to an over head pipe system.
Some people I am working with began to say that they had "had problems" with these and don't like to use them. I don't like these vague "problems", especially when I am being told an entire class of equipment is off limits for use. Yes, the equipment needs to be appropriately applied in order for it to work properly, but unless the concept is flawed I should still be allowed to apply it (properly).
I pressed the issue and was told that there were problems with these pumps failing continuously on a job and some consultant had analyzed the situation and found that the pump steam motive pressure was too high even though the pumps were rated to handle well over the applied pressure. I was further told that reducing the pressure eliminated the repeat failures. But I still was not told what the actual failures were.
I figured that if these pumps as a class of equipment were failing in droves due to "high pressure" I would find some documentation about this plague somewhere. I have not found such documentation. I asked the Spirax-Sarco representative if he had heard of these failure problems and he said he had not (I would expect that if some of his competitors equipment to have trouble, he would say so).
I later heard but have seen no evidence that the pumps in question were failing due to the springs breaking. This would be a low cycle failure mechanism since they were supposedly lasting only a month. The other problem I heard was that these pumps tended to stick, allowing the condensate to flood back into the steam spaces.
The particular brand of pump failing I found out was a Watson-McDaniel. It appears to me that the springs are of Inconel X-750 for corrosion resistance and are in compression. I do not see how pressure directly affects the spring cycle stresses since the pressure does not change the compression or stroke distance.
I suppose higher motive pressure would cause the fluid to be expelled faster and the toggle mechanism to snap faster and harder. This could cause spring resonance ringing every time it was snapped with possible failures at stress concentrations I suppose. The only other thing that would change would be the condensate temperature. The units are rated for 150 psig, meaning the condensate temperature would be a maximum of 366F. I don't think the pressure being used was that high. But I still think I would see some industrial reliability data or conplaints somewhere.
I am tending to think either these were dud pumps and the customer did not have the patience to find out why they were failing, or these problems started after poor maintenance, possibly using springs that were not Inconel x-750.
