Lowering the pump flow rate ?

[fbertaux]

Hi,

We have several chi.bios purchased from LabMaker. They are really cool !

Keeping the ‘native’ pump tubing typically leads to flow rates (when the pump is on) of ~ 1 mL/s in my experience. However we would like for some custom applications to lower this flow rate (by 2-4 fold).

What would you recommend ? I can think of two things and I don’t know if they actually can work:

1. changing the tubing inside the pump to lower internal diameter tubing
2. reducing the frequency of the PWM ? I see from the app.py file this line: sysDevices[M]['Pumps']['frequency']=0x1e #200Hz PWM frequency, what would be the effect of changing this ?

Thanks !

[harrison]

Hello!
Interesting question – I am not sure that your suggestions will work QUITE as you might hope:

1. Changing the tubing MAY be possible, but if you change it too much it will either be too narrow for the pump head (meaning a poor seal will be made and it won’t be able to generate sufficient suction) or the tubing may be too thick leading to the pump stalling since it cannot compress it. Potentially you can work within these limitations – what you would need to do is pick a new tubing with a smaller Inner Diameter (so flow is less), but the same total wall thickness. For example, the current default tubing is is 2.5 Inner/4.5 outer diameter. So, the total wall thickness is 2mm – I believe any replacement tubing needs to keep that quantity constant, otherwise (as I mentioned before) the clearance between the pump head rotor and the wall inside the pump will be wrong. Maybe (for example) you could try 3.5mm outer diameter 1.5mm inner diameter tubing.

2. Changing the PWM frequency won’t help too much – but changing the PWM duty cycle might help you. Currently it is set at 100% when pumps are on. You could reduce this, which will reduce the voltage to the pumps when on, which would in turn slow them down. But, if you reduce it too much the pumps will have insufficient power to start and may stall. Play around with it a bit. TO do this you need to go into the PumpModulation function and change lines:

if (sysData[M][item][‘target’]>0 and currentThread==sysDevices[M][item][‘threadCount’]): #Turning on pumps in forward direction
sysDevices[M][item][‘active’]=1
setPWM(M,’Pumps’,sysItems[item][‘In1’],1.0*float(sysData[M][item][‘ON’]),0)
setPWM(M,’Pumps’,sysItems[item][‘In2’],0.0*float(sysData[M][item][‘ON’]),0)
sysDevices[M][item][‘active’]=0
elif (sysData[M][item][‘target’]<0 and currentThread==sysDevices[M][item][‘threadCount’]): #Or backward direction.
sysDevices[M][item][‘active’]=1
setPWM(M,’Pumps’,sysItems[item][‘In1’],0.0*float(sysData[M][item][‘ON’]),0)
setPWM(M,’Pumps’,sysItems[item][‘In2’],1.0*float(sysData[M][item][‘ON’]),0)
sysDevices[M][item][‘active’]=0

Where you see “1.0*float(sysData[M][item][‘ON’])” reduce the 1.0 to something smaller, say 0.8.

Alternatively you could set up the pump to pulse on/off every second or so which would allow you to have a lower average (but yet still fairly “constant”) inflow of liquid.

Let me know how you get on!

[Author]

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