johannestoger
Bioengineer
Hi,
I'm a medical imaging engineer well outside my comfort zone - I hope you can give some insight on a flow experiment I'm designing.
We're trying to generate a controlled pulsatile flow in a 1" pipe. The peak flow is around 0.6 m/s (2 ft/s), and the pulse should go from zero to peak to zero in about 300 ms. To make this work, I'm considering taking a PVC pipe, putting a piston in it and driving the piston with an electric servo motor. With check valves for the inflow and outflow, we have a simple pulsatile pump, and the servo will hopefully give us excellent control of the flow pulses. The piston will travel about 10 cm (4") at a top speed of 0.6 m/s. The setup should be able to run around 10000 cycles without changing the piston/cylinder seal.
We're pumping against a low pressure, about 0.1 bar (1.5 psi) including the pressure gradient to accelerate the flow in the pipe leading to the experiment. My calculations using the basic course in fluid dynamics from university tells me that this should work pressure-wise. However, the seal between the piston and the cylinder is a big uncertainty for me, especially since we need to run about 10000 cycles without changing it.
So, some concrete questions:
1. Would a simple O-ring on the piston be enough?
2. Can I rely on plain water for lubrication of the seal? Do I need to run the pump with some kind of oil to make this work over 10000 cycles?
3. What is the risk of the seal breaking, i.e. creating a water leak?
4. What kind of friction can I expect in the seal? I need about 4-5 N to drive the flow - will the seal friction be significant compared to this? This is important to know to choose an appropriate servo motor.
5. Is PVC a good material for the cylinder, considering the wear on the seal? Is there some better choice? Anything that's now metal is OK.
Thanks for reading this far, I'd be very happy to hear what you think.
I'm a medical imaging engineer well outside my comfort zone - I hope you can give some insight on a flow experiment I'm designing.
We're trying to generate a controlled pulsatile flow in a 1" pipe. The peak flow is around 0.6 m/s (2 ft/s), and the pulse should go from zero to peak to zero in about 300 ms. To make this work, I'm considering taking a PVC pipe, putting a piston in it and driving the piston with an electric servo motor. With check valves for the inflow and outflow, we have a simple pulsatile pump, and the servo will hopefully give us excellent control of the flow pulses. The piston will travel about 10 cm (4") at a top speed of 0.6 m/s. The setup should be able to run around 10000 cycles without changing the piston/cylinder seal.
We're pumping against a low pressure, about 0.1 bar (1.5 psi) including the pressure gradient to accelerate the flow in the pipe leading to the experiment. My calculations using the basic course in fluid dynamics from university tells me that this should work pressure-wise. However, the seal between the piston and the cylinder is a big uncertainty for me, especially since we need to run about 10000 cycles without changing it.
So, some concrete questions:
1. Would a simple O-ring on the piston be enough?
2. Can I rely on plain water for lubrication of the seal? Do I need to run the pump with some kind of oil to make this work over 10000 cycles?
3. What is the risk of the seal breaking, i.e. creating a water leak?
4. What kind of friction can I expect in the seal? I need about 4-5 N to drive the flow - will the seal friction be significant compared to this? This is important to know to choose an appropriate servo motor.
5. Is PVC a good material for the cylinder, considering the wear on the seal? Is there some better choice? Anything that's now metal is OK.
Thanks for reading this far, I'd be very happy to hear what you think.
