Pump string jammer 4

[itsmoked]

I'm faced with extracting a submersible multi-stage pump whose lift pipe failed about 10 feet down from the top. It's set about 150ft down. I'm thinking I've seen some sort of jamming board that you slide around the pipe string and then as you lower the pipe the weight of the pump string jams the jamming board holding the whole stack against the top rim of the well casing.

Am I just imagining this or does it exist? What's it called?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

bimr, the part of your statement that is incorrect is the the casing is drained to lower the starting load on the motor. A centrifugal pump will experience a higher starting load with an empty pipe than it will with a full one. That is basic physics of centrifugal pumps.

The vertical turbine pumps you linked to are for high flow agricultural or industrial applications and do not have foot valves (check valves at the suction of the pump), which would restrict flow and require maintenance. Without foot valves the casing will drain when the pump stops, and no drain hole needs to be drilled in the piping to do this.

The items in your links are just air vent valves that are required to deal with the problems caused by not using a foot valve, such as air entrainment and water hammer.

The pump we are discussing in this thread does have a foot valve and the well pipe is intended to always be full of water.

 

[bimr]

bimr, the part of your statement that is incorrect is the the casing is drained to lower the starting load on the motor. A centrifugal pump will experience a higher starting load with an empty pipe than it will with a full one. That is basic physics of centrifugal pumps.

The vertical turbine pumps you linked to are for high flow agricultural or industrial applications and do not have foot valves (check valves at the suction of the pump), which would restrict flow and require maintenance. Without foot valves the casing will drain when the pump stops, and no drain hole needs to be drilled in the piping to do this.

The items in your links are just air vent valves that are required to deal with the problems caused by not using a foot valve, such as air entrainment and water hammer.

The pump we are discussing in this thread does have a foot valve and the well pipe is intended to always be full of water.

The part that I did not get right is that the holes are in the check valve, not in the casing pipe.

"8.4 Removal of the pump unit When lifting the pump to withdraw it, take account of the pump weight plus the weight of the water column contained within the riser pipe if the pump unit does not have a check valve with drain holes. (If the check valve does have drain holes the weight of the water column is not applicable.)"

The parts that you are getting wrong are:

[ol 1]
[li]These are submersibles pumps, not vertical turbines. The link was to air release valves which are also commonly used on submersible pumps.[/li]

[li]The check valves are on the discharge end of the submersible pumps, not on the suction side.[/li]

[li]The check valves do not require any more maintenance than the submersible pump does.[/li]

[li]The wells are potable drinking water applications.[/li]

[li]All of these submersible pumps have check valves, not foot valves. Foot valves are usually equipped with some type of strainer which requires maintenance.[/li]

[li]Deep well check valves with drilled holes have to be equipped with air vents to remove the air on pump start-up. Otherwise, the air goes into the potable water system.[/li]

[li]The well column drains back to the level of the aquifer, and is not empty. The pump is not starting against an empty pipe.[/li]

[li]The well casing does not have to be full of water.[/li]

[li]Submersible well pumps have lower starting loads than vertical well pumps. These pumps are commonly equipped with soft starts.[/li]
[/ol]

 

[Compositepro]

bmir, the only point I made was that your statement that "well pipes are drained to lower the starting load on the pump" was not correct.

In response, you posted links to air vent valves for vertical turbine pumps. Now you post a bunch of random stuff tangential to this point of contention to imply that you are "right" and I am "wrong".

Do you still maintain that "On deep wells, the installer will drill a weep hole to drain the casing so that the pump doesn't have to start against the whole water column."?

I'm not going to waste any more time on this topic.

 

[bimr]

bmir, the only point I made was that your statement that "well pipes are drained to lower the starting load on the pump" was not correct.

In response, you posted links to air vent valves for vertical turbine pumps. Now you post a bunch of random stuff tangential to this point of contention to imply that you are "right" and I am "wrong".

Do you still maintain that "On deep wells, the installer will drill a weep hole to drain the casing so that the pump doesn't have to start against the whole water column."?

I'm not going to waste any more time on this topic.

I admitted my mistake above. Why is that so hard for you to do?

 

[Valvecrazy]

Nobody likes pulling a wet string. Pull a 20'-30' section of pipe up in the air, full of water, you are going to get wet when you unscrew it. Over time you learn how to wrap that section to contain the water as much as possible to keep from getting wet. Drilling a hole in the check valve solves that problem. However, even draining back to the static level doesn't let the pump start under enough head or backpressure. It is best to leave the pipe full of water all the way to the top of the water tower or to the inlet to the pressure tank. It is even better to start the pump against a mostly closed valve.

When the weight of the water in the pipe is more than the hoist can lift, or when the water is not clean enough to just let run on the ground. a check valve with a break out pin can be used. In this way there is no hole in the check valve, the pump starts under load, and there is no air to get rid of. When you get ready to pull the pump just drop a short piece of steel pipe down the drop pipe to break off the break out pin. The pin breaks and drains the drop pipe so you don't have to pull a wet string.

 

[itsmoked]

Interesting.. I'd be afraid the thing you drop down the pipe might somehow end up outside the pipe due to a broken pipe or the pipe breaks during the pull out.

We drilled a 3/16" hole at the bottom of each 20 foot pull. I couldn't believe how much force the water had jetting out that hole. Several of us caught splatters that got us good, especially laying on our stomachs drilling the pipe down in the sump. We were loath to turn the dirt we were working on into a mud bog.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

Sorry, bimr I guess you still do not realize what your mistake was that I was pointing out, and therefore I could not understand where you were coming from.

It is a common misconception that reducing the back-pressure on the discharge of a pump will make it easier to start. While this is true for positive displacement pumps or air compressors, it is not true for centrifugal pumps. I think it is very important that misconceptions do not get spread on this site by a lack of challenge to them.

For the benefit of anyone reading this, who is not that familiar with the physics behind centrifugal pumps: all the pump does is spin water in the casing with an impeller. If no water is allowed to leave the periphery of the casing, that water will simply spin, and little power is needed to do this, even though the pressure at the periphery of the pump casing is at maximum (due to the centrifugal force of the spinning water). If water is allowed to leave the casing, then the water that enters must be accelerated by the impeller. It is the acceleration of this mass that requires energy. Thus the more flow there is through a centrifugal pump the more power is required. Pressure is the result of the spinning and does not cause any load on the pump motor.

Therefore draining the well pipe before starting the pump will increase the load on the pump motor due to the high flow into an empty pipe. It will not reduce the load due to lower back-pressure.

 

[Artisi]

A couple of minor points re start of well pumps,
Axial flow units are better started against no imposed head.
A centrifugal unit without check valve will usually have some head imposed resulting from the inlet being below the standing water level.

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.)

 

[bimr]

Compositepro,

Thought you were not going "to waste any more time on this topic".

Pressure is the result of the spinning

But there you go again, posting more incorrect stuff. Suppose another uninformed person reads your posts. Now you are posting that "Pressure is the result of the spinning". Actually, fluid flow is the result of the spinning. A pump guy would say that pumps only create fluid flow as the headloss from the discharge flow is what creates the pressure. Here's a tip for you. If english is not your first language, try having someone proofread your posts.

"A pump does not create pressure, it only creates flow. Pressure is a measurement of the resistance to flow."

As I mentioned the other day, I said I made a mistake and Artisi corrected my mistake. I am going to try to explain this to you one last time.

First off, this situation is unique to deep well pumps. (It is obvious that you have no experience with these pumps.)

On a deep well, the pump check valve has a drilled hole in it to drain the well casing back to the level of the aquifer. Read that again. As Artisi posted, this is to reduce the weight when the casing is withdrawn. For a 1200' casing 12" in diameter, the weight of the steel casing is about 22 tons. If water is in the casing, that adds another 30 tons of water weight. Letting the casing drain shaves 30 tons off the lifting weight when the pump is pulled for maintenance.

8.4 Removal of the pump unit When lifting the pump to withdraw it, take account of the pump weight plus the weight of the water column contained within the riser pipe if the pump unit does not have a check valve with drain holes. (If the check valve does have drain holes the weight of the water column is not applicable.)

There it is, drain holes in the check valves, quoted straight out of the pump manufacturer's operating instructions.

In addition, as I mentioned the other day that these pumps are equipped with soft starts. A soft starter is a solid-state device that protects alternating current (AC) electric motors from damage caused by sudden influxes of power by limiting the large initial in-rush of current associated with motor startup. They provide a gentle ramp up to full speed and are used only at startup (and stop if equipped). So there, you are not going to overload the motor.

Of course, if you were familiar with these pumps, you would know all this. If you can't understand, I am not going to explain this to you again.

 

[Valvecrazy]

Axial or mixed flow pumps are only used for very large submersibles and work completely different than a centrifugal type. Axial flow are more like PD pumps and starting with as little load as possible is good. Centrifugal type pumps start easier against a closed or almost closed valve. There are a few things in the manufacturers operating instructions that are not correct. Drilling a hole in the check valve of a centrifugal type submersible is not good for the pump. Starting with a high static water level helps, but is not nearly as good as starting at deadhead or almost deadhead conditions. Any operating instructions that say drill a hole in the check valve is just as wrong as when they say to install a check valve every 200'. Both of those things cause problems and are hard on the motor.

It is a common misconception that reducing the backpressure on the pump will make it easier to start. I agree with Compositpro that this misconception should get nipped in the bud when possible. It is counter intuitive and hard for people to understand as it is.

I would not describe it as pressure being the result of spinning or head loss creating flow. The fact is, as Compoitpro stated, "If no water is allowed to leave the periphery of the casing, that water will simply spin, and little power is needed to do this, even though the pressure at the periphery of the pump casing is at maximum".

Also, soft starting is not a good thing for motor with Kingsbury type thrust bearings. The hydroplane effect and film of water between the plates on the Kingsbury thrust bearing does not happen until the motor is at least up to 50% speed. The longer it takes to get to 50% speed the more damage to the thrust bearing as it is running dry. And as Compositpro stated, there is very little load on the pump/motor when starting against a closed valve at max head. So, a soft start only benefits the electric company by reducing the inrush current somewhat. But a submersible cannot be slowly ramped up or down like a motor with ball bearings. Therefore, the inrush current is not reduced like it can be when using a standard motor with ball bearings.

I have pulled thousands of wet strings and never drilled a hole in the couplings. The hoist has already lifted the weight for you to be able to drill the hole. Just wrapping the section with a burlap bag or a plastic/rubber sheet can direct the flow mostly back down the well as the pipe is unscrewed from the coupling and lifted out. On wells with contaminated water we would use the check valve with the knock out pins. A 3' piece of 1" sch 40 steel pipe dropped in 2.5" steel drop pipe is just the right diameter and weight to break off the knock out pin at the bottom of a 1200' to 2000' sting. The hoist truck is plenty strong enough to lift the pipe full of water, we just didn't want any of the contaminated water on the ground around the well head.