I need help, gotta fluid engineer in the house

[steverice]

I'm trying to build a pressure sensitive regulator, utilizing a piston over a needle and seat. I have ran into a couple problems on the flow bench and need to talk to a fluid type of engineer, or somebody that might know more than me, (that aint tuff either).









Thanks in advance

s.r.

[Boucher]

It is usually a bad way to start answering a question with another question. What are you trying to do? I have had a stroke and a lot of other medical problems and my brain doesn't work like it should or like it used to so be patient with me.

There is an old Red Jacket Pump Co low flow pressure regulator that was used to prevent pump cycling.There is some similarity between these and your sketches.

Right now I can't remember what it was called. I have a couple of them in storage would be glad to ship you one if it would help. They probably have the paperwork with them. I would be glad to copy that and Email that to you also. If nothing else, You might be able to cannibaize some parts. Let me know if this will help or intrests you.

[boslab]

it would appear that it would blow/dump at atmospheric pressure? in which case isnt the 'regulator' = atmospheric= open ended pipe.
if you add a spring then it becomes a regulator of sorts
looks like a bleed valve for a radiator [in uk] this is with out doubt a good site to get ideas batted around so i mainly replied to give it a bit of a bump and maybe arouse interest, there are a lot of realy clever and talented folk on this site [when they arent bickerring over some esoteric point]
hope you get an answer but theres always the shed, build and try, its what fills my junk box
mark

[TGTool]

This would be my analysis of what happens. In the first sketch the FORCE on the diaphragm (air pressure times diaphragm diameter) must match the FORCE on the needle (oil pressure times needle exposed area). When the force on the oil side becomes greater it lifts the needle, relieving pressure until force on the needle becomes lower than the force on the diaphragm and the needle seats again. I'm not clear on the function of the bleed hole on the air side. If air pressure can't be controlled then a small needle valve for air could allow some control, otherwise it just means lost (waste) air.

In the second instance, essentially nothing changes except that the piston is interposed. Unless the diaphragm is smaller than the piston, the relationship between air pressure and oil pressure will remain the same.

Boslab's reference to a spring references another regulation mechanism. If, instead of air pressure against the diaphragm, you had a spring with a screw adjustment for spring pressure you'd have another mechanically adjusted oil pressure regulator. This arrangement is fairly common.

And you can have both a spring and air pressure. This arrangement might show up in a fuel pressure regulator for a turbocharger system in which the carburetor is inside a plenum with boost pressure applied. A spring regulator sets basic fuel pressure, but when boost starts, this boost pressure is added to the float bowl and opposes fuel pressure so fuel flow will be reduced and eventually stopped. However if a small line is run from the plenum to the spring side of the regulator it will ADD its pressure to the fuel to make sure that the fuel always has its set pressure above boost. And conversely, when the plenum is at atmospheric pressure, the fuel pressure is controlled only by the spring setting.

[barts]

I'd get the dynamic flow effects away from the diaphragm. I built a regulator for steam for our steamboat; here's the working sketch:



The basic idea here is pretty simple. An existing gas pressure regulator has the valve removed and the back tapped for 1/4" NPT. We re-use the diapragm and adjustment bits, spring, etc and the diapragm acts on a reach rod, which lifts a ball off the seat several inches above. This keeps the heat of the steam away from the diapragm, since the steam simply condenses in the 6" length of 1/4" pipe. I used a 3/8" ball end-mill to cut the seat in the stainless plumbing bits for the ball. The only difficulty I have with this is that it sometimes buzzes a bit; this is probably because there's water in the steam.

[philbur]

Some questions:

Why do you need to use air, why not a spring?
What is the source of pressure for the fluid, is it continuos or oscillating?
Is the interest to maintain the upstream fluid pressure or to supply 2 gpm down stream?

A simple system like you describe has the possibility that it will oscillate about the desired pressure/flow. You may need a damping mechanism. These types of control valve are normally regulated by a pilot valve.

Try googling pressure sustaining valve.

Phil

PS: the piston doesn't appear to add anything to the design unless you lose the diaphragm.

[steverice]

Thanks guys,

The reason for not having a spring is that when there is no air pressure, the needle is free to move from the seat allowing unrestricted full flow. So, when there is no air pressure the returning fluid has no pressure, air pressure creates restriction thus pressure.

The bleed hole is there to release air pressure out from the top of the diaphragm, without it air pressure would increase and without the bleed hole it wold simply block itself off at the at pressure.

Different size orifices on the incoming pressure to the diaphragm chamber when coupled with the bleed hole will regulate the amount of pressure. against the diaphragm, thus regulating the fluid pressure.

Problem with air over diaphragm is air turbulence within the chamber and fluid fluctuations, (read chattering). That is the reason I am putting the piston over the top of the needle. I want to remove the air pressure from the diaphragm to better regulate the fluid pressure via, the air pressure.

The piston diameter and diaphragm diameter are the same.

Fluid and air pressure are fluctuating. Sometimes as fluid pressure and air pressure both increase the oscillation of the diaphragm will occur.

There is a constant up and down action of both fluid and air pressure.

It is extrememly important that fluid pressure follows the air pressure at the right ratio.

What is happening on the flow bench...

Fluid pressure is smoothly raised and lowered using the piston, the problem is... Drum roll please... the amount of pressure that the piston type is making over the diaphragm

Diaphragm w/ .040' bleed hole
10lbs of air pressure @ 2 gpm = 35 lbs of fluid pressure.
20lbs @ 2 gpm = 70 lbs fp
30lbs @ 2 gpm = 110 lbs fp

Piston over seat w/ .040 bleed hole (I have tried other larger sizes also, but loose the ratio of increase at higher pressures)
10lb @ 2 gpm = 75lbs fp
20lb @ 2 gpm = 140lb fp
30lb @ 2 gpm = 185lb fp

Since the piston is pushing directly on the needle closed instead of the diaphragm pulling the seat against the seat, I am seeing a drastic increase of pressure exerted on the needle.

Is the area and pressure being exerted by the piston only on the needle instead of the total area of the diaphragm pulling on the seat.

Thanks again.

s.r.

[philbur]

Sorry Steve but the English in the extract below is bad enough that it's not possible to understand what you are saying.

"Since the piston is pushing directly on the needle closed instead of the diaphragm pulling the seat against the seat, I am seeing a drastic increase of pressure exerted on the needle.

Is the area and pressure being exerted by the piston only on the needle instead of the total area of the diaphragm pulling on the seat."

Seems like you need a damping device. This is why commercial systems use the liquid pressure applied to diaphragm together with a restrictor and pilot valve. Air is always going to be very "bouncy". You could possibly add a dash pot concept for damping, as used on SU carburettors.

What happens to the air pressure between the piston and the diaphragm. What happens if the piston leaks.

What is important, 2gpm or constant fluid pressure? Where does the valve vent to, atmospheric?. A complete hydraulic circuit diagram would help.

Phil

Thanks guys,

The reason for not having a spring is that when there is no air pressure, the needle is free to move from the seat allowing unrestricted full flow. So, when there is no air pressure the returning fluid has no pressure, air pressure creates restriction thus pressure.

The bleed hole is there to release air pressure out from the top of the diaphragm, without it air pressure would increase and without the bleed hole it wold simply block itself off at the at pressure.

Different size orifices on the incoming pressure to the diaphragm chamber when coupled with the bleed hole will regulate the amount of pressure. against the diaphragm, thus regulating the fluid pressure.

Problem with air over diaphragm is air turbulence within the chamber and fluid fluctuations, (read chattering). That is the reason I am putting the piston over the top of the needle. I want to remove the air pressure from the diaphragm to better regulate the fluid pressure via, the air pressure.

The piston diameter and diaphragm diameter are the same.

Fluid and air pressure are fluctuating. Sometimes as fluid pressure and air pressure both increase the oscillation of the diaphragm will occur.

There is a constant up and down action of both fluid and air pressure.

It is extrememly important that fluid pressure follows the air pressure at the right ratio.

What is happening on the flow bench...

Fluid pressure is smoothly raised and lowered using the piston, the problem is... Drum roll please... the amount of pressure that the piston type is making over the diaphragm

Diaphragm w/ .040' bleed hole
10lbs of air pressure @ 2 gpm = 35 lbs of fluid pressure.
20lbs @ 2 gpm = 70 lbs fp
30lbs @ 2 gpm = 110 lbs fp

Piston over seat w/ .040 bleed hole (I have tried other larger sizes also, but loose the ratio of increase at higher pressures)
10lb @ 2 gpm = 75lbs fp
20lb @ 2 gpm = 140lb fp
30lb @ 2 gpm = 185lb fp

Since the piston is pushing directly on the needle closed instead of the diaphragm pulling the seat against the seat, I am seeing a drastic increase of pressure exerted on the needle.

Is the area and pressure being exerted by the piston only on the needle instead of the total area of the diaphragm pulling on the seat.

Thanks again.

s.r.

[steverice]

Sorry Steve but the English in the extract below is bad enough that it's not possible to understand what you are saying.

"Since the piston is pushing directly on the needle closed instead of the diaphragm pulling the seat against the seat, I am seeing a drastic increase of pressure exerted on the needle.

Is the area and pressure being exerted by the piston only on the needle instead of the total area of the diaphragm pulling on the seat."

The diaphram will have to pull the needle back into the seat area, looking at the picture I drew (great isnt it?) the fluid pressure is increased when the needle closes up to the seat, after the seat the area of the diaphram on the "wet" side see no pressure at all. So, to close the needle against the seat the air pressure must pull the needle back into the seat area, with the piston it is pushing directly against the needle and fluid pressure.

Seems like you need a damping device. This is why commercial systems use the liquid pressure applied to diaphragm together with a restrictor and pilot valve. Air is always going to be very "bouncy". You could possibly add a dash pot concept for damping, as used on SU carburettors.

What happens to the air pressure between the piston and the diaphragm. What happens if the piston leaks.

In order to keep drag low on the piston there is no seal or ring on the piston, so yes, it does leak around the diameter of the piston. I have machined sufficient reliefs to allow that air to be released.

What is important, 2gpm or constant fluid pressure? Where does the valve vent to, atmospheric?. A complete hydraulic circuit diagram would help.

2 gpm is a testing flow number, and is only a base line used for set up, under use the GPM and pressure vary.

Phil

for what its worth

[aboard_epsilon]

for what its worth

i looked into this the other day

http://bbs.homeshopmachinist.net/showthread.php?t=35087

and decided after spotting them on ebay for £22 ,that it wasn't worth re-inventing the wheel...you could probably find them cheaper than that in the USA.

but that was for my next version ..the pumped only ..no air version

I'm about to test my air pressure model ..the air pressure is regulated by the air regulator ..is it not ?

and what do you need a pump for ..if the air is doing the work ?

the tank should act like an aerosol

with the inlet for the air on top ...and a separate pick up tube that dips into the reservoir of fluid from the top .

you also need a good size filler hole of an inch in diameter....with suitably made screw in plug



all the best.markj