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Diaphragm Compressor - Harmful to Run With Input Closed?

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JonSea

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I salavaged a nice diaphragm vacuum pump and three pressure/vacuum solenoid valves from a hospital-type blood pressure monitor. I may use these to create an improved vacuum pick & place tool. My current version is built out of a nebulizer; the down side is I've used a huge mechanical foot-operated valve to dump the vacuum to release a component. Most solenoid air valves don't work against a vacuum.

One way I can connect the new (to me) vacuum pump and solenoid valve is so that the line to the pickup handle is open to atmosphere to drop a part (controlled by a foot switch). This leaves the diaphragm vacuum pump operating against a closed valve. Is this a harmful condition for the pump? Generally, it would only stay in this state a few seconds each time.

The alternative is to use two valves, so that the pickup is connected to atmosphere as in the compressor input when dropping a part. This slightly complicates things, but if operating against a closed head is detrimental to the compressor, I'll follow this path.
 

dknguyen

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I don't think so, because that's how they work by definition.

In vacuum bagging operations, once the bag is evacuated, the pump continues to operate to maintain that vacuum against small leakages in the bag and seals. That's basically operating against a closed input valve.

The load, however, is larger in this state since it's fighting back pressure from the atmosphere than when it is actively equalizing by passing air through it.

That said, I suppose it's possible if the pump is trying to hold back more pressure (1 full atmosphere) than it was designed to do, but I've never seen a vacuum pump that could not hold back at least 1 atmosphere. I guess it's possible a medical one was designed that way as a failsafe to not harm the patient.

What is the vacuum pump's job in the piece of equipment it was salvaged from? I can't of why a vacuum would be needed. Only an air compressor. Are you sure it's not an air compressor that can be hooked up in reverse to be a vacuum pump?
 
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JonSea

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It's from a blood pressure monitor in its original life, to inflate a blood pressure cuff. Since it's a diaphragm pump, it won't care if used for pressure or vacuum. There are barbs for both the inlet and outlet port on it.
 

dknguyen

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Then it all comes down to whether the maximum back pressure it can hold back/produce is equal to 1 atmosphere.

The diagphram pumps I know of that are explicitly called vacuum pumps can all hold back 1 atm. I suppose the easiest way to tell is to stick connect the outlet in compressor mode straight to a pressure gauge and see if it can reach 2 atm.
 

KeepItSimpleStupid

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Cars have lots of vaccuum solenoid valves (VSV). An 82 Toyota Celica has a number of them. One controls the egr valve. Located on top of the valve cover under the air cleaner.

I believe it's a valve that opens the EGR valve fully when off and it modulates otherwise. There is another that's part of the AC system and opens the outside air damper part way.
Located under the glovebox in the A/C duct to admit outside air.

They are 12 VDC valves.

The other general issue with valves is that they usually need a dryer/oil mister. The VSV's a car naturally have it. It's the valve that's the usual issue that may not be compatable with vacuum.

The vacuum valves I was used to in my work environment were used for High vacuum or ultra High vacuum (1e-6 to 1e-9) Torr and they were bellows type air to open, spring to close or a gate type that were double cylinder air to open/air to close. For some of those valves an electric to air valve was used. They had integral needle valve vent ports on the solenoid valve, so you control the speed of the cylinder.

It was amazing how better the reliability improved when using lubed dry air.

I bought like 20 manifoldable ASCO valves for a project. The coil was 24 VAC. before I could use them, I had to ultrasonically clean them to remove the dust, They were really noisy without the initial treatment. They were ON/Vent types. Venting the mist is a good idea too.
 

KeepItSimpleStupid

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look under "air lubricator"
here: https://www.mcmaster.com/#air-tool-oilers/=1dfs7hj

So, you combine a lubricator, oiler and regulator together. This is primarily used for valves and air tools.

For shop air, you might also want a dryer. A refrigerated dryer is usually the way to go. See https://store.industrialairpower.com/Air-Dryers_c_8.html

For painting you need dry filtered air.

Here https://www.gamut.com/c/power-trans...cu-ft-total-air-capacity-2-iso-class-NjAwNzYx

is a point of use dryer.

Sometime, you also need an automatic line drainer to remove the water at a low point in the system.

So, where I worked at we had the compressor and refrigerated dryer in the machine shop for primarily the sand blaster. There were air outlets at each machine which were primarily used for dust guns,

then the lines traveled about 100 feet or more to an area where pnuumatic valves were used. During it;s trip, we had a automatic vent at it's low point to drain the system of water.

There was a point of use oiler/filter/regulator at each machine.

Most systems were vacuum systems and had local exhaust for the vacuum pump. The exit ports of the valves exited up the exhaust stack. The 4-way valves for the double-acting air cylinders really required the oilers.

Two systems I put together had about 20 on/off valves and two 4-way valves. Only the 4-way valves got the oiler/regulator.
Exhaust was in a ventilated enclosure.

So, you don;t want water in your air lines. The act of compressing air adds water.

You don;t want oil in your lines, but it's needed to lubricate the tools and some valves unless the valves are OK for dry air.
Particulates cause wear.

When painting, you don't want water or particulates in the air supply to your paint gun. This is not something we normally did.

You might use something like this https://www.autobodytoolmart.com/astro-air-control-unit-120cfm-capacity-2618-p-14147.aspx for paint. You might even need dryer air than this provides.

I selected this https://www.asco.com/en-us/Pages/solenoid-valve-series-280-s.aspx series for my 20 or so valve system. Note that it's for air/inert gas. https://www.asco.com/ASCO Asset Library/asco-series-225-280-sub-miniature-catalog.pdf so they don't require lubrication. They did require cleaning before installation 20 years ago.
 

dr pepper

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Diaphragm pumps in industry usually dont need lube, not sure about medical.
If its easy pull it apart and have a look, one issue you might have is noise, if the cam isnt securely fixed to the diaphragm then it might stay clear of the cam a little and rattle against it.
 

KeepItSimpleStupid

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True. The tools the air powers and external valves might.

So, a diaphram compressor is ideal for an air brush or a source of vacuum.
 

JonSea

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With the inlet closed, it actually is much quieter than with it open. It shouldn't be a problem for using as a pick & place - the inlet will only be closed while releasing a part.
 
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