Diaphragm pump Selection

[keerthivasan81]

I am in the process of deciding the AOD pump specification for charging a liquid from a 200 lit barrel to a 7500 lit vessel. The feed port on the vessel is at a height of 4 m from floor level. The liquid is viscous (viscosity: 6500 cp) in nature and pipeline size employed for transfer is 1.5” (discharge side) 2” (suction side) with discharge pipeline length around 7 m.
The pump was mounted at a height of 1.5 m from the floor level. The pump which I have selected gives a much lower flow rate (5 PLM immediately after pump discharge side itself at an air pressure of 6 ksc) which is far lower than my desired charging rate of 20 LPM.
Selected AOD pump details:
Max. Flow rate: 133 LPM; Max head: 85 m (in terms of water)
Diaphragm and ball valve MOC: PTFE
Max air pressure: 8 Ksc.
Feed and discharge port size: 1”.
As per the characteristic curve provided by the manufacturer, the pump delivers around 90 LPM at head of 20 m. I am obtaining only 5LPM immediately after the pump and my dynamic suction head will be around max 10 m
I know that viscosity of the actual fluid employed will reduce the flow rate. But the pump discharge flow rate is less than 10 % of the rated flow rate. I am surprised at the extent of pump flow rate reduction. My questions are:
1. What could be the reason for the very low flow rate obtained?.
2. Will Teflon diaphragm employed and suction lift (presently 1.5 m static) affect the pump discharge flow rate?
3. Any suggestion on selecting a pump of higher order or using the existing pump with any changes

 

[DubMac]

Could the viscosity be impeding flow with too much friction?? If so, maybe try a larger suction line size feeding the pump. Viscosity can also inhibit timely action of the valves in an AOD(balls & seats I'm guessing?) , causing a bit of volumetric loss. Just guessing.

Can't guess what you're suction side piping configuration looks like, but you want it as short and straight as possible.

 

[1gibson]

Manufacturer's characteristic curve is most likely based on water, you have a very viscous liquid. Have you applied viscosity correction factors and still do not get what is expected? Or did you expect to achieve water performance when pumping molasses?

 

[bimr]

Your suction line is too small. The suction line should be 3 times the size of the pump ports. Position the pump as close to (or below) the level of the fluid as possible. Start the fluid slowly using an air valve. Set the air pressure and crack the valve open slowly.

With the viscosity of the fluid that you are trying to pump, you should be able to pump about 40% of the water capacity.

 

[keerthivasan81]

Thanks all for your suggestions. I am herewith attaching the approximate line diagram of my system and characteristic curve of the pump selected for your valuable suggestions:

Application:
The manufactures supplies the viscous liquid in 200 lit MS drums. Our application is to blend the liquid contained in individual drums after charging them in the blending vessels. Two blending vessels of capacity total capacity 7500 lit. and working capacity of 6000 lit are available for this purpose. I am planning to unload the material in the 200 lit MS drum to the blending vessel using AOD pump (Total charging quantity: 6000 lit).
Nature of liquid:
Highly viscous polymer liquid (6500 cp at 30 deg C). The polymer is heat sensitive and I am afraid I shall be able to heat the product. Normally we handle at a maximum temperature of 40 deg C. So the option of heating the liquid to reduce the viscosity is not available to me.
Suction side:
- Corrugated Flexible piping of 2 m (max) was employed
- Flexible Pipe Size: 2”
- Suction Lift: 1.5 m (max)
Discharge side:
- SS pipeline of size 1.5” (Schedule No: 40)
- Total piping length : 7 m (max)
- Pipe fittings: 1 Valve + 4 Elbows + 6 Flanges.
Pump details:
- Max. capacity: 133 LPM ( Flooded inlet)
- Max head: 85 m
- Diaphragm MOC: PTFE
- Inlet/Outlet port size: 1”
(Characteristic curve attached)

I have experimentally calculated the flow rate by opening the flange joint that is immediately after the pump discharge (marked as ‘1’ in the diagram attached). The discharge head would be very little for the above case. It was found to be only 5-6 LPM.
If I assume a total head of 20 m (very high estimate) up to that point ‘1’,As per the characteristic curve, I get a flow rate (at air pressure of 4.8 Ksc) of 90 LPM corresponding to the head of 20 m.

Then why am I getting such a very low flow rate with the actual liquid. (Or Am I missing any factor apart from viscosity?)

Any inputs based on the above data provided will be very helpful to me.

 

[keerthivasan81]

Approximate flow diagram for the above material Charging

 

[bimr]

The corrugated tubing will also significantly decrease the flow capacity.

 

[DubMac]

Another poster was asking what services a PC (Progressive Cavity) pump would typically be used for. Your service would fit a PC pump perfectly.

The I-R ARO pump is a top quality AOD pump that has been around for years. With all due respect, your system is poorly designed. If you are determined to make it work, lower the pump, increase diameter of suction line, and as per bimr get some slick tubing or pipe for the suction line, not corrugated.

Quit worrying about the discharge side of the pump. As with most pumping problems, your worries are on the suction side.

 

[LittleInch]

I agree, your issue is the inlet / suction pipework from what you've provided. The pump needs 2m NPSH, you start with 10, loose 2 for the lift and then 6m left for such a sticky product? Get a smooth inlet tube 3-4" and mount the pump on top of the drum or preferably seal the inlet and roll the drum on its side with a vent hole open at the top.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[keerthivasan81]

Thanks for all your valid comments.

The liquid which I am trying to lift is usually supplied in 220 Lit MS drums by the manufacturer.
There are two ports on the top side : feed port ( ID: around 54 mm) and vent port

Due to the limitation on the feed port size, I am unable to increase my suction line size.
I will try with a slick pipe instead of corrugated one.

 

[bimr]

Your line size does not have to be the same size as the barrel fitting. Install a fitting to increase the pipe diameter at the barrel and decrease the pipe diameter at the pump end of the pipe.