self priming centrifugal pump limitations 1

[someguy79]

I am trying to decide if I can accept a vendor proposal to use a self priming centrifugal pump instead of a vane pump.

The application is for diesel unloading from trucks. Gravity draining is not an option. An air eliminator downstream of the pump will be used.

The concern I have is that the self priming centrifugal may not be able to perform a suction lift from a partially full tanker when the suction line is empty. If the suction line is empty, the air volume may be much larger than the priming chamber. The suction line is estimated to be 10 to 20 feet of 4" pipe and hose with a strainer, some valves, etc.

Is this air volume typically a problem, or will a self-priming centrifugal typically be able to prime itself independent of the suction air volume?

 

[Artisi]

Depends on what type of self-primer, if it is a "wet" self-primer you need to fill the priming chamber with the pumped fluid so that "self-priming" can take place, if it's a vacumm or air ejector assisted "selfprimer" then there is no limit as to the amount of air that can be exhausted in achieving prime.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[someguy79]

What I'm interested in is more like the 'wet' self-primer you describe. I understand that these pumps have a chamber that needs to be at least partially filled before it can begin priming.

I am trying to find out if there is typically any limit to the air volume one of these pumps can handle while priming. Does this chamber fill with air, or will the liquid keep recirculating until it's primed?

 

[keyepitts]

Most of the "wet" self-priming centrifugals that I am familiar with will continue to recirculate the liquid until the air in the line is evacuated, or until enough heat builds up that the liquid in the pump boils.

 

[someguy79]

keyepitts,

Thanks for that clarification. It's exactly what I was trying to find out.

 

[ports394]

someguy79, wet self primers are essentially cheaters when it comes to self priming. You have to fill the housing (somehow whether it's a hole/plug on top, etc) at the beginning. In your case, you'd have to fill it with diesel. And it will spin that until the air is gone.

How about using a double diaphragm pump? Those pumps can move super viscous liquids and pasts even in cold weather. I think that would be ideal for your diesel. They have electric, water, and air driven double diaphragm pumps. But those things will self prime very easily, even if there is a lot of air or a leak. Plus it's a positive displacement pump, which means your diesel will always move forward.

Is flow pulsation an issue for your application? Buy a large pulsation dampener.

 

[someguy79]

I wasn't really looking for a pump to deal with high viscosity because the local ambient doesn't often get below 50F.

I didn't look to diaphram (or double diaphram) pumps because I'm looking to move around 300 gpm. I don't know many diaphram pumps with that kind of capacity.

Positive displacement pumps are generally good for my application because most of them are good at self-priming. However, the piping system also has to handle the pump as a potential source of overpressure. In this case a relief valve routed to the pump suction will serve this purpose. Additionally, a low flow switch will be used for shutdown to protect against overheating/seal failure.

Thanks to all for your replies. I think I have what I need on this issue.

 

[ports394]

McMaster can be overpriced, but they do have 2 pumps listed to pump diesel fuel at 200GPM+ flow rates.


235 gpm, aluminum pump, 9948K24 $2,219.24

235 gpm, stainless steel, 41655K32 $4,713.04

*Note, these require 100 CFM of compressed air.

If you contact a local double diaphragm pump dealer, you can get one to do 300+ GPM. And you can buy something with an electric motor running it. If you can supply that much air, my favorite pump is the Sandpiper from the Warren Rupp. That bad boy will pump rocks and marbles if necessary.