Relationship between a shop vac's power and hose diameter

[jmacmaster]

I have an old 2.25 hp Shop Vac. My wife just bought me a new 5 hp Shop Vac. The new one has a hose that is much larger in diameter than the hose on the old one. I wouldn't be surprised if the increase in the surface area between the opening in the new one's hose and the old one's hose is equal to the increase in hp of the new vac over the old vac. If the two increases (in the hp and the size of the opening in the hose) are equal, it seems to me that the suction on the new vac won't be any more than the suction on the old vac, in which case I'll have gained nothing in terms of what the vacume will pickup off floors, fabrics, etc. I can of course compare the suction of the two and get some idea that way, but so far I haven't had the nerve, as I fear I might be right in my assumption and will be dissapointed. Tho of course I know that I'll have to bite the bullet and do the suction comparison test soon.

Comments?

 

[CBDFrontier06]

It may not suck any harder, but things that you weren't able to suck up with your old one due to size won't affect the new one. That would be as important to me as actual suction. I'm forever removing the hose from mine to dislodge items that I thought should make it. I'm very happy with the suction mine provides, but I can't wait to get a bigger one due to the hose diameter.

 

[jmacmaster]

Yeah, I'd thought about that CBDFrontier06.

 

[kanling]

I think you've got it backwards. Larger hose diameter has a lot less resistance to airflow than a smaller diameter hose.

 

[obbop]

Still can't suck up those pesky neighbor kids even with the 2-1/2 inch hose with 6 powers of a horse providing the suction factor.

 

[labman]

OK, I was all wet about area and holes. I do know liquids and pipes, and I think air follows the same laws. The difference flow from changes in cross section are greater than the changes in area. I mean big, 16 or 32 times as much flow for twice as big of a pipe.

Vacuum moves nothing, it is the air flow. Lots of experience with that. I once managed an operation where we moved a semi load of material through 3 different pneumatic conveyors every shift. Your new vac will move much more air although at less pressure. It will not pick up as heavy of a piece. However, it will pick up lots of anything it can, and as CDB said, larger things will fit through the hose. Stick the end of the new hose in a pile of sawdust. If you don't bury it, watch the sawdust disappear. Bury it too deeply, and no air can get in.

 

[CBDFrontier06]

If you're wanting greater pressure (vacuum) than your old vac, maybe Lowes has a reducer you can use to accomodate a smaller diameter hose. That'd be ideal for me, as I'd like good suction to vacuum out the truck, then use the bigger hose to clean up a woodworking mess in the garage.

 

[XS650]

The new one won't necessarily suck harder but it will suck on a bigger area so it will move more crud into the bin.

Like Labman said, it's the velocity of the air at the nozzle that moves the crud off the floor into the hose.

Once you get past the nozzle there are two important things to consider when sizing the hose. The hose needs to be big enough to not cause too much flow reduction from pressure loss and it needs to be small enough that the air velocity is high enough to keep the crud moving through the hose. There is a fairly narrow range of air velocities that well designed built in shop vac systems are deisigned to have. Portable shop vacs are sensitive to air velocity too.

 

[Matt_S]

FWIW, you can't trust those horsepower numbers. 5 hp is impossible for a normal household outlet. The important thing is suction power and airflow through the hose as labman explained. Your new one sounds similar to my shop vac and I've been very pleased. Having the extra big hose does tend to get the job done faster.

 

[oilboy123]

2.5 inch size vacs are the way to go, in my opinion.

 

[alreadygone]

Have to agree with Mat_S. Horsepower or gallons are totally unbelievable!

Bob

 

[mechtech]

The reason certain vacuum cleaners on TV can pick up a bowling ball is that they use a special large end with a lot of square inches.

 

[kc8adu]

quote:

---

Originally posted by Papa Bear:
The 5 hp job must be a 220v unit.

5 hp = 3730 watts which at 117 volts is 32 AMPS !!

P.B.

---

is it a SEARS vac?
remember the "sears horsepower" on the compressors?
bet they rate the hp on lra.
that is locked rotor(stalled)

[ August 23, 2006, 11:24 PM: Message edited by: kc8adu ]

 

[Papa Bear]

The 5 hp job must be a 220v unit.

5 hp = 3730 watts which at 117 volts is 32 AMPS !!

P.B.

 

[jmacmaster]

UPDATE:

I turned on both shops vacs today and tested the suction of each against my hand and against my
t-shirt where it fits fairly tight against my belly. The new 5 hp one has much more suction power than the old, 2.25 hp one. It has at least twice the suction. I'm quite pleased.

Thanks all for your input.

I took the old one to the local
bar/restaurant/mini-market gathering place (I live in a rural area and this place is somewhat of a community center). I walked in and put a sign on it that said that it was free for the taking. One of my friends was there and immediately walked over, took off the sign, said that he'd just burned out the motor on his shop vac, and took my old one out to his truck. In fact, he and another guy had just been talking about his burning out the motor on his shop vac. What a coincidence.

 

[porcupine73]

It's not entirely unlike an air compressor with a certain flow rate at a given pressure.

The best the vacuums can do is pull absolute vacuum so at best you have air rushing into the end of the hose at 14.7psia or so.

I'm not saying the vacuums can or do pull absolute vacuum and it is doubtful they do with that design, probably a few psid at the most.

Both vacuums might likely generate the same vacuum if the hose is blocked, but the larger unit should have a higher flow rate with the hose unblocked.

 

[Papa Bear]

What porc said.