DRAFTING WITHOUT A PRIMER PUMP

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Permalink Reply by Todd "Walt" Walton on February 19, 2010 at 6:09pm

Alright John, let me make sure I understand. You have the hard suction connected and in the dump tank. You have a line in operation off of tank water and slowly you open the intake valve to suck (Venturi) the air out of the hard suction which in turn allows the water to reach the intake valve. Basically, you use water passing from the tank to pump line into the pump as your primer. Is this correct?

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Permalink Reply by John M. Scheibel on February 19, 2010 at 11:52pm

Yes..You are correct..But understand that this is a Delicate Process, and you may still have to "Pull" on the " Damaged" Primer to help move some Air out of the line..Doing this will reduce the amount of air in the suction line, and depends alot on the size of the Suction Line, and the length of Suction line in the tank..Shorter amounts are better..

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Permalink Reply by Todd "Walt" Walton on February 20, 2010 at 5:04pm

Given a 10' piece of 6" suction with the need to pull water through 6' of the hard suction, impeller eye at 48" (about average) and water level of 24" (full dump tank) how long would this take to prime? Can you do it by circulating tank water or do you have to be discharging? Just curious.

I would also argue that you don't have to use a butterfly valve just as long as the valve you use is opened very, very slowly.

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Permalink Reply by Michael Dombroski on February 21, 2010 at 3:41am

Hi all

We use Ameican pumps down here and we have several methods of "emergency priming" to draft without the use of the priming pump. Here's the two I use to teach pump operation.

1. Tank Circulation method, as mentioned by John. We circulate the water from from the hose line back into the tank supply in order to create the vacuum without using all the tanks water. When the hose line is operating slowly close the tank to pump valve until a vacuum of about -80kPa is showing on the compound gauge (the valve will still be partly open). You then slowly open the suction inlet valve. The compound gauge pressure will rise toward zero. Stop opening the suction inlet when it gets to about -30kPa (for a 3 meter lift). The gauges will fluctuate as the suction hose draws water, but will settle when the prime is achieved. Then you close the tank to pump valve fully, open the suction valve, fill the tank, and rest is history.
2. Blank cap method. Take pump out of gear and close all valves that may let air into the pump. Remove the suction strainer and hold the suction hose slightly above the pump outlets. Open the tank valve to fill the suction hose (or use buckets for a portable pump). Open the outlets valves to remove air until water is flowing. Top up suction hose and lower so the level of water overflows from the suction and screw on the blank cap to seal (not too tight). Put the suction in the water, put the pump in gear, increase pump speed, close the tank valve. Remove the blank cap slowly while it's under the water with the pump pressure at around 500kPa (80psi). Open hose line outlets slowly as requires and replace the strainer.

These are good training drills just to provide some variation to pump training. I've never had a primer failure on the job, mostly because I'm in an urban environment, but its good to try these things out so you can get to know your pump.

Cheers
Mike D

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Permalink Reply by J. Eric Anderson on August 7, 2011 at 3:59pm

The way I was taught seems slightly different but has the same principle of creating a venturi to evacuate the air from the pump. Just another tool for the tool box in case your primer pump does not work.

1. set up for normal drafting operations.

2. place a nozzle on a rear discharge and open the bail.

3. place engine in pump, back fill the suction hose by pulling "tank to pump" valve.

4. set RPMs to approx. 1200 and open the discharge with the nozzle.

5. slowly feather in the "tank to pump" valve. You will see the gauge fall into vacume then jump up to 50-100 psi. Also look for the hard suction to drop if attatched to drivers side of pump. Sometimes you need to featther in the discharge as well depending on how the pump is layed out. Once the preasure jumps completely close the tank to pump and fully open the discharge. Then start filling your tank. Typically takes 200-300 gallons of water.

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Permalink Reply by William Hoehn on September 2, 2011 at 8:24am

Most of the suggestions for achieving prime submitted by previous posters are valid methods.  If we consider how a "Self Priming" trash pump achieves a prime we will also understand the method being used in this thread.  A trash pump has an additional waterway that brings water from the discharge chamber back to the intake (eye) of the impeller.  As this water enters the impeller, it is combined with air from the suction tube and the combination is discharged back to the discharge chamber.  These air bubbles break and are discharged to the outlet of the pump while the water makes another trip back to the intake.  Eventually the air is all removed from the suction tube and a hard prime is achieved. 

Taking this technique to an engine with a primer problem, the water source could be the tank water or from a separate supply such as a portable pump from the water source.  When using tank water it is a fallacy to believe that pulling the tank to pump line will fill the suction tube.  The air in the tube is trapped and the tank water will simply run down the bottom of the tube and out the strainer, while the air remains trapped in the tube.  Removing the strainer and putting a blind cap on the end before pulling the tank to pump will then fill the suction tube and force the air up through the pump to a discharge (must be open to let the air out).  Keeping the end of the suction under the water, engage the pump and it is now possible to remove the cap and reattach the strainer.  This is not usually a viable solution because it is difficult to stand in a river or pond.

If we open a discharge (tank fill or a hose line) we can entrain the air and water.  Taking the mixture back to the tank prevents the loss of water and allows the tank to act like the discharge chamber on the trash pump.  Discharging to a hose line allows the line to keep fighting fire, but risks the entire operation should the priming attempt fail.  Many tank to pump valves leak, and once the water is gone from the tank, there can be a significant air leak from the tank to the pump.  This leak will be difficult to locate (lift the tank lid and listen inside), and the problem is only solved when enough water to cover the leaking valve is returned to the apparatus tank. 

The method of using a portable pump can work should the pump operator encounter this condition and dropping the tank does not solve the problem.  It is well to remember that as long as there is any pressure on the master gauge, air can not go into the pump from an open discharge.  Too many times I see pump operators who, upon loosing prime, close all discharges, even though the pump is still producing 10 to 20 psi.  This is the result of learning from old time pump operators who were originally taught pumping using a centrifugal pump with a drive-line operated primer.  These old devices required the pump operator to disengage the main pump (centrifugal) and engage the primer pump to refill the pump with water.  The primer was connected to the highest point in the pump casting.  When the primer was operated the water filled the pump, then the pump was shifted into gear and pressure was achieved.  Todays pumps have the primer line attached near the eye of the impeller, so that even when some pressure is being supplied, the "slug" of air near the eye can be removed by pulling the primer handle.

The key to achieving a prime with a directly connected hard sleeve (no buttrefly valve) is to move a fairly large amount of water, while choking back on the water supply, but you must maintain master discharge pressure.  With 3 joints of suction and a full 10 foot lift, it is seldom that a prime is achieved with a single tank of water when discharging back to the stream or pond. (You will need a protable pump)  Generally the only hope for getting prime is to keep the tank fill wide open and slowly choke back on the tank to pump, while not loosing all the discharge pressure.  Play around with all of your equipment.  Every design difference will cause a different sort of problem.  Some will prime easily and others you will swear a blue streak.

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Permalink Reply by Todd "Walt" Walton on September 11, 2011 at 1:14pm

William, I have to disagree with this part of your statement "When using tank water it is a fallacy to believe that pulling the tank to pump line will fill the suction tube.  The air in the tube is trapped and the tank water will simply run down the bottom of the tube and out the strainer, while the air remains trapped in the tube."

You are correct that when the tank to pump valve is pulled water will run down the suction tube and back into the water source.  You are also correct that this flow of water will not fully fill the suction tube.  You are also correct that placing a blind cap on the suction tube will allow it to fill completely.  What I am disagreeing with is that you can achieve a draft by using tank water to start filling the hard suction and then idling up the pump which causes the water to reverse direction and start drafting from the water source.  As I stated previously, this is a very delicate maneuver but it can be done.  I have witnessed it and I have done it.

 

Thank you,

Walt

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Permalink Reply by Todd "Walt" Walton on September 11, 2011 at 9:40pm

After I made the previous post I was thinking about what had been discussed about using a blind cap to fill the hard suction and Williams statement about it being difficult to stand in a river.  I thought about the possibility of putting a clapper valve on the end of the hard suction which would allow you to back fill the hard suction and then start drafting.  Of course if you used a clappered Siamese with two 2.5" inlets you would get quite a bit of restriction which would reduce the volume you could deliver.

Of course this brings up the next question.  Does any manufacturer that you know of offer a low level strainer with a clapper valve or something similar that would allow you to transition from draft to tank and back to draft without losing prime? 

 

Thanks,

Walt

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Permalink Reply by Larry Lasich on September 11, 2011 at 11:04pm

What's a clapper valve and why would you need it for going back and forth from tank to draft?

Todd "Walt" Walton said:

After I made the previous post I was thinking about what had been discussed about using a blind cap to fill the hard suction and Williams statement about it being difficult to stand in a river.  I thought about the possibility of putting a clapper valve on the end of the hard suction which would allow you to back fill the hard suction and then start drafting.  Of course if you used a clappered Siamese with two 2.5" inlets you would get quite a bit of restriction which would reduce the volume you could deliver.

Of course this brings up the next question.  Does any manufacturer that you know of offer a low level strainer with a clapper valve or something similar that would allow you to transition from draft to tank and back to draft without losing prime? 

 

Thanks,

Walt

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Permalink Reply by Todd "Walt" Walton on September 11, 2011 at 11:44pm

A clappered valve is similar to a back flow preventer.  It allows water to move in one direction only.  With a clappered Siamese you can attach one supply line from the first pumper that will start flowing water into LDH but not out the other side of the Siamese.  When the second pumper is available it can connect a line to the other connection and start feeding into the supply line along with the first pumper.  If both engines are supplying the same amount of water both clapper valves will be open.  Same concept as a FDC.

To my way of thinking if the low level strainer had a clapper valve you would not lose prime when you shut off your hard suction because the water would not be able to flow back into the tank.  When you opened up the valve to the hard suction the water would be there waiting for you and you wouldn't have to re prime to draft.  In an ideal set up you won't lose prime when you shut the valve to the hard suction but when most apparatus get some age on them the valve leaks or you may have an air leak in the connections somewhere that causes you to lose prime.  The clapper valve would keep this from occurring.

Hope this answered your question.

Walt

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Permalink Reply by Larry Lasich on September 12, 2011 at 4:40am

From a draft tank, I run an 1.5 to the low foot.  From a static open source, I hang a garbage bag from the handle so that it hangs near the surface.  The hard suction stays filled under pressure and I can control it from the gate valve and I have a waste line running to maintain prime.

The only time I've seen a clapper is on a small wildland engine and I thought the restriction was excessive.
Todd "Walt" Walton said:

A clappered valve is similar to a back flow preventer.  It allows water to move in one direction only.  With a clappered Siamese you can attach one supply line from the first pumper that will start flowing water into LDH but not out the other side of the Siamese.  When the second pumper is available it can connect a line to the other connection and start feeding into the supply line along with the first pumper.  If both engines are supplying the same amount of water both clapper valves will be open.  Same concept as a FDC.

To my way of thinking if the low level strainer had a clapper valve you would not lose prime when you shut off your hard suction because the water would not be able to flow back into the tank.  When you opened up the valve to the hard suction the water would be there waiting for you and you wouldn't have to re prime to draft.  In an ideal set up you won't lose prime when you shut the valve to the hard suction but when most apparatus get some age on them the valve leaks or you may have an air leak in the connections somewhere that causes you to lose prime.  The clapper valve would keep this from occurring.

Hope this answered your question.

Walt

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