Looking for a suitable pump

[driga]

Hello all,

I would like to know which pump should I use for the following application:

1. Working fluid: Glycerin-water (91% glycerin) + liquid crystal (for temperature measurement)
2. Flow rate: should be high enough
3. Exit pressure : 8-12 bars

What we have now is a peristaltic pump that can only generate an outlet pressure of 2.5 bar. The reason for having peristaltic pump is to avoid mechanical contact between the pump (e.g.: centrifugal pump) with the liquid crystal (since it is temperature and shear sensitive).

Much of the peristaltic pump (medium size one) cannot reach the desired exit pressure. That is why I am curious whether there is other pump that is suitable for my application. One more thing, the pump should have a gentle pumping action.

Thank you.

 

[ione]

There diaphragm pumps which can easily handle the discharging pressure you're looking for. Now the problem is to define what is a "high enough" flo rate

 

[Artisi]

High enough is about the same as adequate.

 

[jistre]

Just slightly more than not quite enough, though.

 

[Artisi]

But less than too much

 

[driga]

The maximum flow rate range from 50-70 l/min.

 

[ione]

Now the flow rate is defined I confirm , there are diaphragm pumps available for your specs.

http://www.udor.it/public/prodotti/182_pt_Catalogo AGRICOLTURA 2009 10.pdf

 

[driga]

Ok, could you give the link for the diaphragm pump?
Is it possible that our peristaltic pump cannot generate enough pressure due to lack of power from the electric motor?`

 

[ione]

In my previous post I’ve added a link concerning a diaphragm pump (Italian brand Udor -

http://www.udor.it/home.php)

which is rated for pressures up to 20 bar.

Further to your peristaltic pump: how is it rated (head and flow rate)? This is the first thing to check.

 

[jistre]

driga,

It is possible that the motor is undersized, though it would be one of the things way WAY down on my list to consider since these types of pumps are often sold paired by the manufacturer with a very specific motor for the pump's capabilities. I'd start looking at the pump you have and determine whether the pump itself is undersized for the application.

If the manufacturer's head rating for the pump is lower than the head you're looking for, it's likely got an internal relief valve to protect the pump that will open before you are able to hit your target head. In that case, no matter what motor you slap on the pump, it won't be able to deliver the desired head until the internal relief either fails or you overcome its relief capacity, at which point you're just asking for a failure.

With a PD pump, overspeeding the pump to get more head or flow just isn't a great idea in my opinion. The fact that they're constant volume devices (as opposed to the constant head of a centrifugal device) means that if they're driven hard enough so that the system cannot accept the flow being put into it, they can and will generate massive overpressures very quickly. They just are far less forgiving than constant head machines when driven against downstream restrictions. By speeding the pump up to get the head you require, you can quickly overcome the mechanical limits of the pump.

Now, if the pump is rated for the head you need and you can't get it at full speed, then look at the pump. However, because this is a constant volume device, if the pump is running at full speed, that already means the motor is able to deliver the power required to pump that volume against the system resistance.

 

[driga]

The pump manufacturer said that the peristaltic pump that we have right can generate up to 2.5 bars. So the head is round about 25 meters.

My task is to test the pump first. The system consists of reservoir (slightly above the pump's inlet, about 40 cm). The outlet of reservoir is 3/4" inch with a ball valve. It is then connected to an expander from 3/4" to M36 and the a hose (1 meter length) with ID of 25.4 mm.

The hose is connected with a self-made adapter. A box shape with a size of 80 x 80 x 180 mm. It has one hole M26 on the one side of the long-side and another 4 holes (M26) at the other side. The reason is that the pump can accommodate up to four channels. Then the pump, another self made adapter. Then 1,2 meters hose (25.4 mm ID) and a screw type flow meter.

I have asked the flow meter company. He gave me an example that with a working fluid having a kinematic viscosity of 35 mm²/s and flow rate of 20 l/min, the pressure loss in the flow meter will be 1.5 bar. So even when I use only 2 channels with 96 rpm (40% of max rpm), the pump gave me an overload error.

I calculated my system using bernoulli, excluding the flow meter loss, I arrived at 1.08 bar of needed pressure at the exit of the pump. So with a loss of 1.5 bar in flow meter, it would be make sense that I have an overload.

Please correct me if there is something wrong with the calculation.

Thanks.

 

[micalbrch]

Not sure whether I really understand your problem. But you have an oberload error with your pump. That means you have an overload error with the motor. And that means that flow and/or pressure are too high for the pump with this motor. The pump manufacturer says the pump is good for 2.5 bar. You want 8-12 bar. So, your existing pumps is way to small. 8-12 bar is good for a diaphragm pump, especially for a piston diaphram pump. Make sure that you get a slow running one (< 100 strokes/min). An appropiately sized pulsation dampener will reduce the residual pulsation down to 5 % or less.

 

[TenPenny]

Remember that a peristaltic (or any other positive displacement pump) doesn't 'generate' pressure, it simply overcomes pressure...so if your flow rate is 'enough', it's doing what it should.

But you still may have an issue finding a peristaltic pump to do such a high pressure (it would be hard to squeeze any tube strong enough to withstand 8 bar...)