How piston valves are measured.

[Technician1002]

When searching to compare performance of 2 inch piston designs with my 2 inch quick dump valve, I found many 2 inch valves are really 1 or 1-/2 inch and I needed to compare to the 3 inch valves with a 2 inch barrel.


I've noticed a trend on spudfiles that piston valves are measured by the diameter of the piston The rest of the industry measures their valves by the diameter of the valve orifice. For example a 3/4 inch QEV has a 3/4 inch port. The piston is larger. Is there a reason we don't use port size here?

[Biopyro]

Not really, just that often when someone makes a valve, they'll be thinking "hmm 50mm piston so it's a 50mm piston valve" sgort and others selling piston valves do list them by port size though. I think it tends to be just a common mistake as opposed to a set protocol. Lots of the more experienced spudders will correctly classify their valves though.

[MrCrowley]

I just do it through habit as I was probably confused back in the day when there was no set 'protocol'.

[King_TaTer]

Yeah I have noticed that over the duration of my time here. If I were you I would construct a "2 inch piston" yourself to see if it really stacks up against your quick dump valve. This would allow for consistency and accuracy when testing the two valves.

[Brian the brain]

I always refer to the port size.

The only reason I could see to do otherwise is to brag.

So I quess I have a 2 inch porting 3 inch pistonvalve...

[Hotwired]

There is no standard.

But what is generally said is:

X inch piston valve with Y porting.

Which is more telling than just one number.


You could for example have a 3" piston but only 2" of porting, that would not be the same as a 2" piston with 2" of porting.

[Technician1002]

There is no standard.

But what is generally said is:

X inch piston valve with Y porting.

Which is more telling than just one number.


You could for example have a 3" piston but only 2" of porting, that would not be the same as a 2" piston with 2" of porting.

I've noticed this. Some valves are not specified by the orifice, but by the size of the pipe they connect to. I've seen this a lot in small ball valves where the actual port is smaller than the pipe. You have to watch this if you need the full diameter for flow or projectiles.

***EDIT***
I modified a 1 inch PVC ball valve to use as a breech loader on my marshmallow cannon. The 1 inch gum balls won't fit in the valve.

I grabbed the calipers. The gumballs I have are 1.02 inches and the ball valve is 0.990. So close, but no go.
They fit the barrel very nicely

[Ragnarok]

I personally always refer to the seat diameter of the valve, but have a habit of qualifying it like saying 1.5" porting piston valve.

The reason I do this is that as far as piston valves are concerned, while the piston's overall diameter affects opening time, the magnitude of the variations between different (well made) piston valves has minimal effect on the projectile's velocity. The seat diameter however has affects flow, which has a big effect on the projectile's velocity.

In other words, two piston valves with 1.5" porting, one with a 3" piston and the other with a 2" piston will have similar performance.
Two piston valves with a 2" piston, one with 1" porting, the other with 1.5" porting - the latter will be noticeably more powerful, assuming the barrel can support the flow.

Hence, I'm more interested in the seat diameter than the piston diameter.

[Technician1002]

Yeah I have noticed that over the duration of my time here. If I were you I would construct a "2 inch piston" yourself to see if it really stacks up against your quick dump valve. This would allow for consistency and accuracy when testing the two valves.

I've considered that, but currently working on a 3 inch 200 PSI valve. I'm more interested in how that performs against the 2 inch.