Centrifugal pump - suction reducer - drain required

[oje002]

Hi

I'm wondering, if you have a drain on the pump itself, is it necesary to have a low pint drain on the suction side then?

The pipeline is horizontal and with the same elevation on both suction side and discharge side, so a drain in the pump will empty all the liquid in the pipeline.

http://tinypic.com/r/11azp6x/5

 

[HPost]

If this is a centrifugal pump and the drain on the pump in on the bottom of the volute, that will be the lowest point of the system. Pulling this plug will drain all of system, assuming that air can get in to replace the fluid in the line.

HPost

 

[pennpiper]

It depends on the size of the pump drain, the size of the whole system and the amount of time you have available to drain the system.

The pump manufacturer would normally put the smallest drain possible for the area available at the bottom of the pump and to meet their requirement for hydro testing the pump assembly in the factory.

If your system is a very large volume and you may want to drain it fast then you should consider your own drain and size it appropriately. Depending on the commodity and the local Codes for contamination, you may also want to consider connecting it to a closed Pump-Out system

prognosis: Lead or Lag

 

[Artisi]

Most process pumps I've come across don't have a case drain in the bottom of the volute, why introduce a potential stop for erosion. Now if it were a cast iron water pump it might well be a different story.

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.)

 

[TenPenny]

A lot of manufacturers make the drain an option, so it's often omitted because purchasing focuses on the dollars, and $100 saved is golden. However, you'll find that most maintenance guys would like to have it; there's nothing like trying to remove the back pullout from a pump, and having several gallons of hot black liquor pour out all over the baseplate, your tools, your feet, etc, when you could use a casing drain to let it drain out directly to the floor and gutter.

 

[LittleInch]

Is it necessary to have a piping drain and a pump drain - probably not

Is it a good idea? probably not. Why -

1) as noted before size is normally pretty small on a casing drain
2) Any dirt sitting in the bottom of your pipe then goes through the pump
3) You then need to pipe your pump drain and put a valve on it otherwise with a plug you risk crossing the threads and needing to get a new pump casing - much more time and expense compared t putting a drain point on
4) The pump drain will be much lower than your pipe - even harder to get a slope on it back to the drain point or even get a bucket / container under it
5) Your new pump might not come with a drain (as noted they are optional) and then you're stuffed.

My motto: Learn something new every day

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

 

[Pumpsonly]

You did not mention the size of the tank and the pump. You will also need to have a valve installed next to the tank out let and also before the pump suction flange. Otherwise you will also drain off the whole tank when you open the casing drain.
The pump casing drain is usually small sized for draining the pump volute.

 

[bingopin]

Some thoughts on pump casing drains for pumps handling hydrocarbons or other chemicals.

Process operators both love and hate casing drains. While insuring complete pump drainage and increased prepping flexibility, they are also potential leak points and could be additional fugitive emissions points. By design, they are usually small diameter and easily plug up.If the drain is routed to an open chemical sewer, it is also an additional entry on the cap and plug list.

Typical ANSI ductile iron process pumps would require a threaded connection to the bowl.Our specs would require the first nipple to be xxs in order to maintain the corrosion allowance at the threaded connection. This makes the plugging issue worse.

API pumps would require a socket welded connection to the pump bowl. This would also require a flange or union to allow for pump casing removal.

Retrofitting a casing drain requires the casing to have a boss cast in at the drain location.

As everyone has pointed out, while there are pros and cons of casing drains, but you almost have to have them on top suction pumps.

 

[LittleInch]

Oje002, looking at your title, you don't give us any details of this reducer. If it's a concentric reducer into the pump inlet then part of your suction line won't drain if flat entry. If it's a bottom flat one then maybe it will.

My motto: Learn something new every day

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

 

[oje002]

It's a bottom flat reducer

 

[LittleInch]

Then it might work, but unless your inlet pipe is quite short (5m or so), I still think this is a bad idea and I think most of the other posters think the same...

My motto: Learn something new every day

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