Primed Intake for Vertical Turbine Pump?

[WhiskeyJack]

Hi Everyone, I am a newbie to this site.

I was hoping someone out there has seen (or possibly designed) a vertical turbine pumping system with the intake directly connected to the pump suction as per H.I. Standards Figure 9.8.10 - Example 4 (see attached) and used in conjunction with a vacuum or liquid priming system.

This project is for a client that would like to retrofit an existing 40 year old wet well that is hydraulically connected (most of the time) to an adjacent lake. Unfortunately the lake, during extreme low water levels, currently operates much lower than what the wet well was originally designed for. We would like to convert the existing wet well into a dry well to accommodate a direct plumbed VT pump suction/intake pipe as per the above referenced H.I. intake configuration. Under normal lake conditions the minimum submergence levels for the proposed vertical turbine pumps can be achieved without priming. However during extreme low lake levels, a priming system (preferably a vacuum system) would need to be used to prime the pump(s) prior to initiation. The worst case NSPHa at the pump(s) would be approximately 7.5m (absolute). We have found several manufacturers with VT pumps that only require 3.5m NPSHr at our design flow. So we will have more than sufficient NPSH available.

Has anyone in their travels seen a vacuum priming system used with this style of pump? Any insight into the above described configuration would be greatly appreciated.

Sean

 

[bimr]

There are three types of vacuum priming systems. The first is a simple educator type used with water or air to remove the air from the main pump casing and to draw liquid from the wet well. The second type is a dry vacuum pump with a protective tank installed between the vacuum pump and the main pump. The tank is equipped with an electrode. Before starting this system, water must be emptied from the protective tank. When the vacuum pump is energized, a vacuum is created in the tank, so air and the liquid is drawn from the main pump casing. When the protective tank fills with liquid from the main pump casing to the low level of the electrode, the vacuum pump is automatically de-energized and the main pump is primed. The third type is a package system that basically consists of one or two water displacement, wet type vacuum pumps, vacuum tank, vacuum valve, vacuum relief valve, water level switches, and pressure switches and gauges. The wet type pump is dependent on a continuous supply of clean service water, which enters the vacuum pump on the suction side, is discharged with the compressed gas, and thus draws air and water from the vacuum tank, main pump casing, and wet well. The device then shuts down automatically.

 

[WhiskeyJack]

Hi bimr,
Thanks for the excerpt from the Pumping Station Design 3rd Edition for available vacuum priming options. I have also found it an excellent design manual.

I was hoping to get feedback on a vacuum priming system used specifically in combination with a vertical turbine pump with the intake installed in the drywell configuration shown on H.I. 9.8.10 - Example 4 (see attachment).

Thanks

 

[bimr]

The text for example 4 was not attached.

Have not seen this arrangement but it should work. The question will be how long does it take to evacuate the air as well as how many times per day or week that the evacuation needs to be done.

One of the most important aspects of pump intake design is the removal of trash from the water. Trash not only refers to solid materials such as driftwood and plastic containers, but also marine plants and animals which can find their way into the intake system. I assume you have some type of screening.

 

[Artisi]

Nothing new or difficult, if using the fig 4 arrangement.
You simply need a rising pipe connected to the inlet pipework terminating at the top of your drywell with a priming tank. I would use a vacuum pump with a float level operating system. Closed to atmosphere when unprimed and opening to atmosphere once the level rises to the preset height in the tank. The vacuum pump could be arranged to shut down once the pump is primed or allowed to run with the float gear cycling open / shut if the water level in the tank fluctuates (probably unlikely unless air is being entrained from the water supply).
View attached:

http://ameripumps.com/pump-functions/

-- this shows the priming system in action. You can probably purchase the “valve gear” section as a separate item from them or others supplying very similar product, if not available I can probably assist you.

Rough sketch of the installation recommendation attached.

Note: the kicker is that a NRV is needed on the discharge of the pump otherwise air will be drawn back thru’ the discharge side of the system and you will never prime the pump.


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.)

 

[WhiskeyJack]

Thanks Artisi and bimr,

We were actually thinking of installing the vacuum priming connection immediately downstream of the vertical turbine pump's discharge head located on the main-floor. This would allow us to prime through the pump column and pump impeller stages and eliminate the need for a dedicated riser pipe. A low profile level instrument (possibly a thermal flow switch or electrode?) would be installed in the pump column immediately downstream of the last impeller stage. Artisi, we had discussed the riser pump configuration you have proposed. Since there will be long radius elbow at the pump suction, the vacuum priming of the riser will not guarantee that the water column will sufficiently prime the first impeller stage.

Bimr, as for the intake it will consist of three (3) Johnson style screens sized with a 2.5mm mesh opening size. The screens would have sufficient area to limit the approach velocity to 0.038m/sec to conform to the local fishery standards. The lake water quality is excellent, so based on the above we don't foresee any issues with debris (other than minor amounts of silt) entering the pump intake.

I realize vacuum priming of a vertical turbine pump is quite unusual but was hoping someone out there had seen this configuration used with success elsewhere.....

 

[Artisi]

I don't see anything unusual in anyway, a pump is a pump is a pump, I also don't understand why the pump won't be fully primed if the priming tank is positioned above the impeller section of the pump unit. This is a similar arrangement used in sewage pump stations requiring pumps to prime / reprime.

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.)

 

[MJCronin]

Whisky,

Vacuum priming of a vertical turbine pump is a standard configuration for the Cooling Water (also called circ water) pumps in an open cycle power plant. Circ water pumps are the massive pumps that circulate lake/seawater etc through the plant's main condenser. Priming pumps are, of course, only used during startup.

Vacuum pumps are the best way to fill the system during startup. I have seen liquid ring pumps in this duty in a Swedish Nuclear Power Plant.

An important part of the startup sequence, these vacuum pumps are sometimes part of a system called "Water Box Priming" pumps.....

See the following:

http://www.pp-s.com/Files/SIHI/Vacuum Pumps and Systems for Power Industry.pdf

Please give us more details of your final configuration.....

MJCronin
Sr. Process Engineer

 

[MJCronin]

http://uniquesystems.com/wp-content...pvs-80025011-wps-waterbox_priming_systems.pdf

MJCronin
Sr. Process Engineer

 

[Artisi]

You could use a small self priming pump connected into the vertical unit as a startup priming unit.

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.)

 

[WhiskeyJack]

Thanks MJCronin and Artisi,

Thanks everyone for your input. Please see the attachment for the proposed pumping and vacuum priming system concept. Any additional comments would be appreciated. It would be great if someone has a project reference or example where a similar configuration has been utilized successfully.

Whiskey

 

[Artisi]

Would suggest something on the priming system would be more beneficial than a pipe, valve and control system layout.

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.)