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Piston valve size

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Piston valve size

Unread postAuthor: Ragnarok » Sat Aug 07, 2010 8:38 am

I thought I'd open this one up for discussion.

Piston valve sizes usually get listed one of two ways.
a) By barrel port diameter.
b) By piston diameter.

Now, the former of these makes sense. Porting diameter and valve flow are directly linked, so knowing this number tells you a lot about the performance of the valve.

The latter, which seems pretty common, makes a lot less sense. Piston diameter has relatively little result on end performance.
In fact, a higher number is usually bad - opening force on a piston is dependent only on seat diameter, but a higher diameter piston will be almost certainly be heavier, accelerate more slowly, and thus take longer to open.
Ideally, a piston's diameter should be as little over the seat diameter as it can be (i.e. the valve still works).

Ultimately, my question is to those people who list their piston valves by piston diameter.
You see, I see these topics in the showcase that say 3" piston valve cannon or something similar, go and look, then find that the cannon is really only what I would consider a 2" valve.

Yes, it is a 3" piston, but we list QEVs, sprinkler valves, burst discs, ball valves, and so on and so forth by their port diameter, not largely irrelevant diameters of internal parts.

Is it not time we started to standardise things so piston valve size was defined in the same manner as it is for everything else?
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Last edited by Ragnarok on Sat Aug 07, 2010 10:22 am, edited 1 time in total.
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Unread postAuthor: JDP12 » Sat Aug 07, 2010 9:09 am

Hm. Interesting idea and I like it. Myself and SB15 were just having a discussion about this last night (seat diameters). I do like that idea.
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Unread postAuthor: velocity3x » Sat Aug 07, 2010 10:52 am

Ideally, a piston's diameter should be as little over the seat diameter as it can be (i.e. the valve still works).


Exactly! A piston larger than necessary impares performance and is totally unecessary.

Is it not time we started to standardise things so piston valve size was defined in the same manner as it is for everything else?


Yes! If a valve has a 4" piston yet a 1" seat......it's only a 1" valve!

I find some of the threads are difficult to follow because of the terms people are using like "porting piston valve". Is a "Porting Piston Valve" new and better than just an ordinary piston valve? Isn't it a prerequisite of every valve to have ports in order to be a valve? "DCV" has become the term for what? Is it a solenoid valve, mechanical valve, what? They've all had names since the day they were invented so why not use them so other people will understand what you're trying to describe? And what exactly is a QDV other than a piston valve by another name?

Yes...standardization would be great!
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Unread postAuthor: Technician1002 » Sat Aug 07, 2010 11:25 am

This discussion does come up once in a while. I list mine by the valve port size as that is what the flow sees. I list my Mouse Musket as a 1 inch even though the piston diameter is 1.5. The QDV's are easy to list as the diameter and port is the same size.

http://www.spudfiles.com/forums/how-piston-valves-are-measured-t17971.html
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Unread postAuthor: SpudBlaster15 » Sat Aug 07, 2010 12:33 pm

I always list piston valves based on the diameter of the greatest internal flow restriction, which is almost always the barrel port. This simply makes sense, as the mass flow rate is the primary factor linked to valve performance.

Ragnarok wrote:Is it not time we started to standardise things so piston valve size was defined in the same manner as it is for everything else?


Yes, it should be, but I doubt you'll have an easy time implementing a standardized piston valve dimensioning system of any kind. Some people will still be inclined to describe their designs based on the diameter of the housing, as this measurement typically applies to several dimensions, including the piston diameter and valve inlet diameter.

If someone can figure out an effective method for implementing a standard system, then by all means do so.

velocity3x wrote:I find some of the threads are difficult to follow because of the terms people are using like "porting piston valve". Is a "Porting Piston Valve" new and better than just an ordinary piston valve?


When a person uses the term "Porting piston valve", it is typically preceded by a number which indicates the diameter of the barrel port. Descriptions such as this are used for exactly the reason Rag describes - The current piston valve rating system is all over the place. It shouldn't be necessary to add extra terms to your description to make it clear what you're referring to, but at this point in time, doing otherwise often leads to confusion and misinterpretation.
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Unread postAuthor: Ragnarok » Sat Aug 07, 2010 2:30 pm

Technician1002 wrote:This discussion does come up once in a while.

Yes, I did recall some former discussion, but couldn't actually dig up the thread. My search-fu was wanting, it seems.
But with the benefit of a link, we can see that thread of yours is now over a year old now - yet it's still happening enough to have prompted me to bring it up again.

It's ridiculous that piston valves get measured by a different (and pretty useless) set of rules, and it's time to put a stop to it.

SpudBlaster15 wrote:If someone can figure out an effective method for implementing a standard system, then by all means do so.

Horribly flaming anyone who does it different. :tongue3:
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Unread postAuthor: MrCrowley » Sat Aug 07, 2010 4:00 pm

Yes, it is a 3" piston, but we list QEVs, sprinkler valves, burst discs, ball valves, and so on and so forth by their port diameter, not largely irrelevant diameters of internal parts

To be fair, usually their connection ports are also the same as their seat.

Also a 1" sprinkler valve has a seat of 1.1" (according to some folks at SpudTech). :roll: :D

I've been in the habit of describing them by piston housing nominal diameter (not piston size) rather than porting, not sure why, just have.
On another note, even when people describe the porting of their piston valve, it is common to say the nominal diameter of the pipe and not the actual inside diameter. 1.5" PVC here is about 45mm in inside diameter which is closer to 1.7" in porting diameter.

I prefer it being described as piston housing size because it makes it easier when searching if you are looking for topics about building a particular sized piston. Doesn't help if it just says "1.5" porting".
You could say that this is not about making it easier to search, then I would say that it doesn't really matter at all because the topics where the housing size and not porting size is listed, will have the porting size described in the topic. If it doesn't, it can be assumed it is the barrel diameter.
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Unread postAuthor: Ragnarok » Sat Aug 07, 2010 5:57 pm

MrCrowley wrote:To be fair, usually their connection ports are also the same as their seat.

And usually a piston valve's barrel connection is the same size as the piston seat. I'm not really seeing a big difference here.

Sure, the chamber connection may be a different size, but in the same vein as the end of your post, that can normally be assumed to be the same as the chamber diameter. And, even in the cases that it's not, unless it's actually the main constriction in the valve, it's not that important.

And as far as pilot diameter... I can't see people wanting valves to be listed by pilot diameter.

Also a 1" sprinkler valve has a seat of 1.1"

It's nominal diameter, sure, but that's still more accurate than listing it as 1.5" or 2", or whatever size the diaphragm in these things is. (Let's play spot the guy who's never used a sprinkler valve.)

Yes, I'd ideally prefer to work by actual diameter, but if you get away from nominal diameters, things run the chance of getting more confusing.

I prefer it being described as piston housing size because it makes it easier when searching if you are looking for topics about building a particular sized piston.

Let's be honest, with the search system on this forum, all you can really do is search for things you know are there. Searching for general information on a subject is nearly impossible.

The reason why the veterans can use the search but the newbs can't is more they know the post is there than because they know the search is there.
If I'm looking for information on something, it usually takes recalling some of the specific wording of the post (or one in the same topic), then a few searches to try and track down the right post.

Doesn't help if it just says "1.5" porting".

I'm not necessarily saying that I have no interest in knowing piston diameter - I'd still like to see it in the topic. I do not however see it as a valid system for measuring a piston valve's size.

It's completely contrary to the way all the other valves we use are measured. Yes, there are valid reasons for wanting to know a piston diameter and I think it should still be listed, but that doesn't mean that it should be considered the standard measurement.
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Unread postAuthor: motorfixer1 » Sat Aug 07, 2010 7:17 pm

I must agree with SB 15 here I would always think that the appropriate way to list the flow rating of any valve would the point of most restriction. The standard of commercial valves is not exactly the best, the commercially available 1/2" ball valve is more like .375" (at is smallest), and so forth. So there is a lot of room for confusion for the folks who arent familiar with the actual sizes. (And the folks who see it every day!) Standard for me is the actual flowing passage.
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Unread postAuthor: Technician1002 » Sat Aug 07, 2010 7:19 pm

To add confusion to the mix, the valve seat size can be larger than the port size. This may be the case with some sprinkler valves with a 1.1 inch seat. The port inside the seat could be smaller. I have not measured one. A good test would be to blow a 1 inch Lemonhead through it. :D

As an example, the Mouse Musket has a 1.5 inch piston that seals on a 1.25 inch o ring valve seat and feeds a 1 inch barrel. For size, I list it as a one inch piston valve. For piston ratio, to calculate pilot pressure when the piston valve opens, I use the OD to Seat Diameter.

The Dragon is a 2.5 inch valve with a 3 inch piston. :D
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Unread postAuthor: Ragnarok » Sat Aug 07, 2010 8:46 pm

motorfixer1 wrote:The standard of commercial valves is not exactly the best, the commercially available 1/2" ball valve is more like .375" (at is smallest)

Well, I may be pretty spoiled, because I only ever work with full bore ball valves.
Even so, they turn out to be something like 19.9mm when it's a 20.3mm ID pipe, but I have the resources to grind them out to a true full bore - it's not a big difference, but when chasing the results I am, it doesn't hurt.

Technician1002 wrote:To add confusion to the mix, the valve seat size can be larger than the port size.

It can indeed be. HEAL's piston valve has a 20.3mm port and a 22.1mm seat (with a 26.2mm piston).

I tend to think of it as a 22mm valve (as the flow at the seat is a greater constriction than the smooth transition down to the 20mm used for the barrel) but I tend to qualify it further if explaining it. Either way, it packs a hell of a punch.
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Unread postAuthor: Technician1002 » Sat Aug 07, 2010 9:25 pm

Unfortunately the Mouse musket did not use a smooth transition from the seat seal into the barrel, so it remains a 1 inch valve. I do have future plans for a 4 inch valve with a smooth transition into a 2.7 or 3 inch barrel. :D I want to find out how fast I can launch an empty pop can.
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Unread postAuthor: MrCrowley » Sat Aug 07, 2010 9:30 pm

but we list QEVs, sprinkler valves, burst discs, ball valves, and so on and so forth by their port diameter
Remember that no one is really saying the diameter of the piston but the nominal diameter of the piston housing. As far as I see it, it's the same as a 1" sprinkler valve, which has 1" threaded port connections albeit a larger (or smaller?) seat/port and a much larger sized piston. A piston in a 2" tee will (usually) have 2" socket/threaded ports, a smaller diameter piston and an even smaller diameter seat. So if we were using the same describing method as with a sprinkler valve or QEV, it would be a 2" valve.

I'd be pretty certain a sprinkler valve would still be called a 1" sprinkler valve even if the seat diameter was only 3/4" but the porting still 1". Now there's the argument of porting vs seat diameter. In your above post you say yourself you class HEALs piston by the seat and not the port. Technician has explained that the barrel porting isn't always the same diameter as the seat, so should be be saying a 1.5" piston valve has a 1.5" porting or a 1.5" seat (99% of the time i'm sure they're the same nominally)?

So my stance on this is that it doesn't really bother me at all. Describing a piston by the seat or porting diameter is probably better but either way you do it (seat, port, housing diameter), i'm sure the other two that weren't described in the topic title will be described in the topic itself.
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Unread postAuthor: Ragnarok » Sun Aug 08, 2010 9:05 am

MrCrowley wrote:So if we were using the same describing method as with a sprinkler valve or QEV, it would be a 2" valve.

No. If we're being strictly honest, we refer to sprinkler valves and QEVs in such a fashion because that's how they're nominally named.
The benefit of this is that their nominal port diameter usually correlates well with their performance, even between manufacturers.

It doesn't matter if that 3/4" QEV has a 1" piston, or a 1.5" piston. End performance will be similar.
When you take two valves with 2" pistons, but one has a 1" port and the other a 1.5" port, end performance will NOT be similar.

What I am saying that a piston valve's nominal size should be tied to the most relevant port diameter - the one where it correlates with performance, allowing better comparison with other valves.

As it is, given how similar QEVs and piston valves are, when we say 3/4", that should really represent two equivalent valves.

I'd be pretty certain a sprinkler valve would still be called a 1" sprinkler valve even if the seat diameter was only 3/4" but the porting still 1".

Probably, but it's not, and anyway, most people wouldn't go to the effort of measuring it specifically. And nominal diameter of the ports/seat is better than the nominal diameter of the piston housing.

In your above post you say yourself you class HEALs piston by the seat and not the port.

Yes, but it's in the same vein as using say a 2" (porting) Mauler valve with a 1.7" golf ball barrel.
It doesn't downgrade the size of the valve to use a smaller barrel.

In HEAL's case, the difference is that the reduction in diameter happens to be soldered to the part that includes the valve, rather than the part that includes the barrel.

In the more optimised HEAL 2 (where the valve is one of the parts I have actually completed), it tapers down from 22mm to 20mm diameter over about 2cm (it's only about 1 cm in HEAL 1), and it's a completely polished transition. That, compared to the restriction of flow through the valve, is irrelevant. Even with the carefully designed valve internals, I'd have to pinch down to 18mm or less before the reduced diameter even risked being significant.

And indeed, that completely flawless transition means the extra valve diameter is actually used, as compared to the likely fairly poor transition used in an average 2" valve to GB barrel case.

The way it's designed means it's possible to either think of it as a top-end 22mm valve (to the extent that it could probably match up against a good 25mm piston valve), or an almost impossible 20mm valve. As its performance is more in line with a 22mm valve than what you'd expect from a 20mm valve, that's why I think of it that way.
If others want to think of it as a 20mm valve - sure, that's a way to do it.

but either way you do it (seat, port, housing diameter), i'm sure the other two that weren't described in the topic title will be described in the topic itself.

That's not really the matter at hand. I want to get to the point that when someone says 2" piston valve, there's not ambiguity over what size that's referring to.

As the barrel port diameter is the most relevant to performance, it would be the sensible way to standardise it.
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Unread postAuthor: MrCrowley » Sun Aug 08, 2010 6:26 pm

Hmm yeah I guess you are right. To save time we could start describing piston valves with a fashion such as: 1.7"x2"x3", meaning it has a 1.7" seat, 2" porting and a 3" housing. Or if you think piston diameter is more relevant than housing you could swap the two. Though I don't see that catching on, just thinking out loud :wink:
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