Super Soaker Central forums

Silence · 05-12-2008, 05:33 PM

Both, really. In either an APH or a CPH, a wider pump will always need more force after a set number of pumps, and because it fills the volume quicker, it will actually become harder to pump earlier than you'd expect.

To answer your question, a wider pump in a CPH would exert a high but somewhat constant force. There actually is some dropoff, so the force will increase a little as you pump, but not noticeably.

Drenchenator · 05-12-2008, 05:37 PM

The pump shaft diameter always determines how much force is need to pump, but you can use a larger diameter pump on a CPS gun. CPS has constant pressure and doesn't actually build pressure like an air pressure gun. The pump gets hard in an air pressure gun because the pressure in the chamber gradually increases because the air volume decreases. When water's pumped into a rubber bladder, the bladder expands and maintains a certain pressure. If more water is pumped in, it expands more--but the pressure doesn't change much. And since the pressure doesn't change, the pump force will be about the same for each pump.

In a nutshell, the pump width always determines how hard it is to pump, but it doesn't matter nearly as much in a CPH because each pump increases the volume of the bladder, not the pressure like in an air pressure system.

aEx155 · 05-12-2008, 06:10 PM

So, on a CPS gun, it would be about as hard to pump near the end as it is in the beginning, right?

Ben · 05-12-2008, 06:16 PM

Yes. You can assume the pressure is constant in most CPS because the pressure is constant enough. In rubber CPS there is some drop off, but it is minor. HydroPower (Buzz Bee Toys' CPS alternative) is an exception to this rule because from what I've read it's between previous CPS and air pressure in drop off.

mr. dude · 05-12-2008, 08:09 PM

But being a 3/4" pump, it would still be quite a bit harder to pump than a 1/2", right?

Ben · 05-12-2008, 08:27 PM

Yes, it would be harder. Going by reported pipe diameters, for the same pressure, 3/4 inch pumps would be 75.5% harder to pump than 1/2 inch.

I would suggest reading this article if you want to learn about how much force a pump takes: http://www.sscentral.org/physics/pump_dia.html

The force is essentially the operating pressure multiplied by the area of the pump. That's all you need to know. If you increase or decrease the area, it affects the force required.

CROC · 05-12-2008, 09:04 PM

By area, is it internal or external diameter we are talking about? My pump would be CPVC, since I have tons of it lying around. I know it would be harder to pump, but with a CPH, that has the same tubing as Mr. Dude's, but it's only about 6" long. I'll do some calculations later, because at this time I am on my Wii, and it takes a long time to reply to messages.

aEx155 · 05-12-2008, 09:07 PM

If you're using CPVC, wouldn't it break, since it isn't pressure rated? The force needed to pump the gun up would eventually break the pipe, right?

Silence · 05-12-2008, 09:45 PM

Internal diameter is what matters. CPVC is a bit narrower, so 3/4" CPVC is between 1/2" and 3/4" PVC in internal diameter.

CPVC may or may not be pressure rated. I personally wouldn't use it for the pump since (A) it's easy enough to get suitable pipe and (B) there's always the possibility of rupture, as you said. But on the other hand, pipe of such small diameter can take much higher pressures. For example, 1/2" pressure rated Schedule 40 is rated to 600 PSI. So it's your call.

Is the pipe pressure rated? What does CPVC when it breaks? If CPVC shatters like PVC, it's not safe; if it just splits like ABS, it should be fine.

aEx155 · 05-12-2008, 09:54 PM

Quote:

CPVC may or may not be pressure rated. I personally wouldn't use it for the pump since (A) it's easy enough to get suitable pipe and (B) there's always the possibility of rupture, as you said. But on the other hand, pipe of such small diameter can take much higher pressures. For example, 1/2" pressure rated Schedule 40 is rated to 600 PSI. So it's your call.

I'm pretty sure that, because of its thinner walls, this ("...pipe of such small diameter can take much higher pressures.") wouldn't apply to CPVC. Does anyone know?

CROC · 05-13-2008, 03:18 PM

Honestly, in Canada, it's hard to find actual pipe lengths of the normal PVC.
There shouldn't be a great pressure buildup in the pump though, so it should be fine.

The pressure rating is very wierd. Here is the equation on the pipe:
(690kPa-82c)/(2760kPa-22C) Or, in PSI:
(100PSI-180F)/(400PSI-73.4F)

FYI, 3/4" CPVC has an internal diameter of 7/16, radius of 7/32

If I have a pump with a length of 6", the area is 9.01 squared inches.
Is the pressure the pressure required for the LRT to inflate, or is it something else?

Drenchenator · 05-13-2008, 04:04 PM

The listed pressure is the operating pressure--it's both the pressure to inflate and the pressure it releases at. You don't get anything out that you didn't put in, so it's the same. No magical increase or decrease.

CROC · 05-13-2008, 04:33 PM

So according to that, it's 30 PSI.

So F=P*A
A 6 inch pump,
F=30PSI*(9.01"squared)
F=270.3 (What unit is this in?)
Or is area simply the internal area, not volume? The volume of the pump is 9.01, and the area is 1.5021826625 square inches.

Drenchenator · 05-13-2008, 04:52 PM

It's internal area. Volume is length cubed; area is length square. Completely different.

Remember, 1.5 square inches is the area of a rectangle with one side being 1.5 inches and the other being 1 inch. Is that really how large you want your pump to be?

I think you accidentally multiplied all of your numbers by ten, or at least it seems like that. I'll explain the how to get the force anyway though.

The diameter as you gave is 7/16". The area of a circle based on the diameter is (pi/4)*d^2. The area is .15033 square inches. The volume for a 6 inch cylinder with this as the base is then .9020 cubic inches. The overall length of the pump doesn't go into the calculation of the force at all, only the calculation of the volume.

Since psi means pounds per square inch, multiplying by the area gets the force needed to get that pressure. Remember dimensional analysis? The square inches cancel, leaving you with just pounds.

(30 lbs/in^2)*(.15033 in^2) = 4.5099 lbs.

Easily doable because the pump area is so low.

An interesting thing to note is that the product of pressure and volume gets the work done. The proper units for the answer you found would be inch-pounds, a measure of energy. This would be how much energy it would take to complete a pump.

CROC · 05-13-2008, 05:49 PM

I think you lost me there. Why would it be length squared for area? Isn't the formula for area of a cylinder pi(r^2)h?

05-12-2008, 05:33 PM	#61
Silence Administrator Join Date: Apr 2006 Location: Virginia Posts: 3,246 UserID: 576	Re: Question Both, really. In either an APH or a CPH, a wider pump will always need more force after a set number of pumps, and because it fills the volume quicker, it will actually become harder to pump earlier than you'd expect. To answer your question, a wider pump in a CPH would exert a high but somewhat constant force. There actually is some dropoff, so the force will increase a little as you pump, but not noticeably. __________________ Forum Rules

05-12-2008, 05:37 PM	#62
Drenchenator Administrator Join Date: Jun 2004 Location: Maryland Posts: 715 UserID: 320	Re: Question The pump shaft diameter always determines how much force is need to pump, but you can use a larger diameter pump on a CPS gun. CPS has constant pressure and doesn't actually build pressure like an air pressure gun. The pump gets hard in an air pressure gun because the pressure in the chamber gradually increases because the air volume decreases. When water's pumped into a rubber bladder, the bladder expands and maintains a certain pressure. If more water is pumped in, it expands more--but the pressure doesn't change much. And since the pressure doesn't change, the pump force will be about the same for each pump. In a nutshell, the pump width always determines how hard it is to pump, but it doesn't matter nearly as much in a CPH because each pump increases the volume of the bladder, not the pressure like in an air pressure system. __________________ The Drenchenator, also known as Lt. Col. Drench.

05-12-2008, 06:10 PM	#63
aEx155 Senior Member Join Date: Apr 2008 Posts: 283 UserID: 1517	Re: Question So, on a CPS gun, it would be about as hard to pump near the end as it is in the beginning, right?

05-12-2008, 06:16 PM	#64
Ben Founder Join Date: Mar 2003 Location: Maryland Posts: 5,974 UserID: 1	Re: Question Yes. You can assume the pressure is constant in most CPS because the pressure is constant enough. In rubber CPS there is some drop off, but it is minor. HydroPower (Buzz Bee Toys' CPS alternative) is an exception to this rule because from what I've read it's between previous CPS and air pressure in drop off. __________________ email: ben at sscentral dot org / Forum rules Read this page before emailing me. Do not send me a PM or email with a water gun question if someone else could answer the question. Post at the forums. You will get a response from me along with others' views or ideas. Do not send me a PM or email about reading a certain post unless it's been a few days since you've posted. I try to read every post.

05-12-2008, 08:09 PM	#65
mr. dude Senior Member Join Date: Apr 2006 Posts: 126 UserID: 572	Re: Question But being a 3/4" pump, it would still be quite a bit harder to pump than a 1/2", right?

05-12-2008, 08:27 PM	#66
Ben Founder Join Date: Mar 2003 Location: Maryland Posts: 5,974 UserID: 1	Re: Question Yes, it would be harder. Going by reported pipe diameters, for the same pressure, 3/4 inch pumps would be 75.5% harder to pump than 1/2 inch. I would suggest reading this article if you want to learn about how much force a pump takes: http://www.sscentral.org/physics/pump_dia.html The force is essentially the operating pressure multiplied by the area of the pump. That's all you need to know. If you increase or decrease the area, it affects the force required. __________________ email: ben at sscentral dot org / Forum rules Read this page before emailing me. Do not send me a PM or email with a water gun question if someone else could answer the question. Post at the forums. You will get a response from me along with others' views or ideas. Do not send me a PM or email about reading a certain post unless it's been a few days since you've posted. I try to read every post.

05-12-2008, 09:04 PM	#67
CROC Senior Member Join Date: Mar 2006 Location: Ontario, Canada (GTA) Posts: 287 UserID: 569	Re: Question By area, is it internal or external diameter we are talking about? My pump would be CPVC, since I have tons of it lying around. I know it would be harder to pump, but with a CPH, that has the same tubing as Mr. Dude's, but it's only about 6" long. I'll do some calculations later, because at this time I am on my Wii, and it takes a long time to reply to messages. __________________ ~CROC~(c 'rock)n. -The master of ideas, and the occasional mod (Works with mr. dude) Mods: 3xA combat - CPS Turbine - Super Flash Flood - (working on CPH)

05-12-2008, 09:07 PM	#68
aEx155 Senior Member Join Date: Apr 2008 Posts: 283 UserID: 1517	Re: Question If you're using CPVC, wouldn't it break, since it isn't pressure rated? The force needed to pump the gun up would eventually break the pipe, right?

05-12-2008, 09:45 PM	#69
Silence Administrator Join Date: Apr 2006 Location: Virginia Posts: 3,246 UserID: 576	Re: Question Internal diameter is what matters. CPVC is a bit narrower, so 3/4" CPVC is between 1/2" and 3/4" PVC in internal diameter. CPVC may or may not be pressure rated. I personally wouldn't use it for the pump since (A) it's easy enough to get suitable pipe and (B) there's always the possibility of rupture, as you said. But on the other hand, pipe of such small diameter can take much higher pressures. For example, 1/2" pressure rated Schedule 40 is rated to 600 PSI. So it's your call. Is the pipe pressure rated? What does CPVC when it breaks? If CPVC shatters like PVC, it's not safe; if it just splits like ABS, it should be fine. __________________ Forum Rules

05-13-2008, 03:18 PM	#71
CROC Senior Member Join Date: Mar 2006 Location: Ontario, Canada (GTA) Posts: 287 UserID: 569	Re: Question Honestly, in Canada, it's hard to find actual pipe lengths of the normal PVC. There shouldn't be a great pressure buildup in the pump though, so it should be fine. The pressure rating is very wierd. Here is the equation on the pipe: (690kPa-82c)/(2760kPa-22C) Or, in PSI: (100PSI-180F)/(400PSI-73.4F) FYI, 3/4" CPVC has an internal diameter of 7/16, radius of 7/32 If I have a pump with a length of 6", the area is 9.01 squared inches. Is the pressure the pressure required for the LRT to inflate, or is it something else? __________________ ~CROC~(c 'rock)n. -The master of ideas, and the occasional mod (Works with mr. dude) Mods: 3xA combat - CPS Turbine - Super Flash Flood - (working on CPH) Last edited by CROC : 05-13-2008 at 03:23 PM.

05-13-2008, 04:04 PM	#72
Drenchenator Administrator Join Date: Jun 2004 Location: Maryland Posts: 715 UserID: 320	Re: Question The listed pressure is the operating pressure--it's both the pressure to inflate and the pressure it releases at. You don't get anything out that you didn't put in, so it's the same. No magical increase or decrease. __________________ The Drenchenator, also known as Lt. Col. Drench.

05-13-2008, 04:33 PM	#73
CROC Senior Member Join Date: Mar 2006 Location: Ontario, Canada (GTA) Posts: 287 UserID: 569	Re: Question So according to that, it's 30 PSI. So F=PA A 6 inch pump, F=30PSI(9.01"squared) F=270.3 (What unit is this in?) Or is area simply the internal area, not volume? The volume of the pump is 9.01, and the area is 1.5021826625 square inches. __________________ ~CROC~(c 'rock)n. -The master of ideas, and the occasional mod (Works with mr. dude) Mods: 3xA combat - CPS Turbine - Super Flash Flood - (working on CPH)

05-13-2008, 04:52 PM	#74
Drenchenator Administrator Join Date: Jun 2004 Location: Maryland Posts: 715 UserID: 320	Re: Question It's internal area. Volume is length cubed; area is length square. Completely different. Remember, 1.5 square inches is the area of a rectangle with one side being 1.5 inches and the other being 1 inch. Is that really how large you want your pump to be? I think you accidentally multiplied all of your numbers by ten, or at least it seems like that. I'll explain the how to get the force anyway though. The diameter as you gave is 7/16". The area of a circle based on the diameter is (pi/4)d^2. The area is .15033 square inches. The volume for a 6 inch cylinder with this as the base is then .9020 cubic inches. The overall length of the pump doesn't go into the calculation of the force at all, only the calculation of the volume. Since psi means pounds per square inch, multiplying by the area gets the force needed to get that pressure. Remember dimensional analysis? The square inches cancel, leaving you with just pounds. (30 lbs/in^2)(.15033 in^2) = 4.5099 lbs. Easily doable because the pump area is so low. An interesting thing to note is that the product of pressure and volume gets the work done. The proper units for the answer you found would be inch-pounds, a measure of energy. This would be how much energy it would take to complete a pump. __________________ The Drenchenator, also known as Lt. Col. Drench. Last edited by Drenchenator : 05-13-2008 at 06:00 PM.

05-13-2008, 05:49 PM	#75
CROC Senior Member Join Date: Mar 2006 Location: Ontario, Canada (GTA) Posts: 287 UserID: 569	Re: Question I think you lost me there. Why would it be length squared for area? Isn't the formula for area of a cylinder pi(r^2)h? __________________ ~CROC~(c 'rock)n. -The master of ideas, and the occasional mod (Works with mr. dude) Mods: 3xA combat - CPS Turbine - Super Flash Flood - (working on CPH)

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