No worries, glad to help
- Thread starter p0689109
- Start date
I finally got round to taking the head off today. All the springs and plate valves seem fit for use as does the bores and pistons. The head gasket stayed on the cylinder block and is undamaged so I am hoping that works OK.
So from the bits in the head when the compressor reaches the pressure set by the controller air is allowed to flow to the two diaphragm valves and their plungers extend and hold the flap valves in the closed position.(These are the ones that, on the heads cylinder side, have a ring of holes) All very well, but does that not mean that the air that is then trapped in the cylinders and cannot escape is in fact acting as a lock loading the compressors motor? Obviously I realise that the piston/ring combination is not a total seal and some air will escape through there and the pump cannot act as a pump as there is no flow i.e the same volume of air is being compressed each rotation. So does the pump strain or idle in that situation or am I missing something?
So from the bits in the head when the compressor reaches the pressure set by the controller air is allowed to flow to the two diaphragm valves and their plungers extend and hold the flap valves in the closed position.(These are the ones that, on the heads cylinder side, have a ring of holes) All very well, but does that not mean that the air that is then trapped in the cylinders and cannot escape is in fact acting as a lock loading the compressors motor? Obviously I realise that the piston/ring combination is not a total seal and some air will escape through there and the pump cannot act as a pump as there is no flow i.e the same volume of air is being compressed each rotation. So does the pump strain or idle in that situation or am I missing something?
Bill Edwards
Member
- Messages
- 4,959
- Location
- Scarborough, North Yorkshire
I think you will find that the diaphragm valves open the inlet valve, rather than holding the outlet valve shut.
At least, that's how I've seen them before and can't think of any reason why anybody would do it any differently as that's the obvious approach, the air is then free to go in and out of the intake with no real resistance.
At least, that's how I've seen them before and can't think of any reason why anybody would do it any differently as that's the obvious approach, the air is then free to go in and out of the intake with no real resistance.
There are 4 valves two of which are inlet valves(the ones with the drilled holes and are spring loaded open, these are the ones operated by the rods) and two are outlet valves spring loaded closed. So you are saying the controller allows air to the inlet valve plate valve against the spring to close the valve doing so by extending the rod through its diaphragm. When the set pressure is reached the controller then removes this feed and so the rods retract and the air is not compressed. But that means that air has to be compressed for the controller to use to move the rods down. But in its state of rest the compressor plate valves are open not allowing it to compress the air. So we have a chicken and egg situation! Until the rods extend through the medium of the compressed air the compressor produces, the compressor cannot produce any air until the rods are extended! So how is that overcome?
Bill Edwards
Member
- Messages
- 4,959
- Location
- Scarborough, North Yorkshire
To be honest I can't make out what it what from the pictures, and trying to think things through from reading your posts is giving me a headache as I simply can't picture it all!
I can't immediately picture why the inlet valves are sprung open, obviously they have to close somehow when the piston is on the up stroke to compress the air and force it out to the receiver.
All I can suggest is that the type I have encountered before have it where the diaphragm valve is screwed in/fixed above the inlet valve.
A little spring inside this keeps the rod lifted so it isn't pressing the inlet valve and the compressor works as normal and compresses air.
When it reaches the set pressure the controlling valve sends air to these diaphragm valves and puts the air to the top of the rubber diaphragm. Doing so pushes it and the rod under it down against the inlet valve, holding it open and thus enabling the compressor to spin without ever compressing anything due to the open valve.
Maybe your compressor has things arranged differently but I expect the same idea will be used. If you really cannot figure it out at all then I suggest cleaning everything, replacing suspect seals and assembling everything, then just giving it a go!
I can't immediately picture why the inlet valves are sprung open, obviously they have to close somehow when the piston is on the up stroke to compress the air and force it out to the receiver.
All I can suggest is that the type I have encountered before have it where the diaphragm valve is screwed in/fixed above the inlet valve.
A little spring inside this keeps the rod lifted so it isn't pressing the inlet valve and the compressor works as normal and compresses air.
When it reaches the set pressure the controlling valve sends air to these diaphragm valves and puts the air to the top of the rubber diaphragm. Doing so pushes it and the rod under it down against the inlet valve, holding it open and thus enabling the compressor to spin without ever compressing anything due to the open valve.
Maybe your compressor has things arranged differently but I expect the same idea will be used. If you really cannot figure it out at all then I suggest cleaning everything, replacing suspect seals and assembling everything, then just giving it a go!
There is nothing wrong with the plate valves or springs and hopefully everything will work when I reassemble it all now that I have bought the motor and pulley. It is just that I would like to know how it is supposed to work in case it does not as I do not know the history of the machine. Your reasoning is the same as mine I believe on how the rod works and when it extends but because the inlet valves are spring loaded open when at rest I am assuming the rod extension closes them when the set pressure is reached. I am calling them the inlet valves because they are on the side of the head that is marked IN and has the air filter screwed into it and the other side valves, which are spring loaded closed with the big 3/4 inch whitworth headed plugs, are on the side of the head which has the outlet pipe to the tank. The diaphragm valves are screwed in and have some a degree of adjustment with a lock nut arrangement.
I think I might have worked out how the inlet valves work. If the controller allows air to the inlet valve from 0 to full controlled pressure then the valves will be held closed against the spring pressure and the compressor will in fact deliver compressed air to the tank. When the controller reaches the preset pressure required then it kills the feed to the inlet valve diaphragm/rods and the spring opens the plate valves and the compressor just idles!
Bill Edwards
Member
- Messages
- 4,959
- Location
- Scarborough, North Yorkshire
So, it's working backwards to normal in that it cuts off the supply to the diaphragm valves to make the compressor spin with no load... new one to me!
You have got it **** about face, the compressor runs till it reaches the pre set pressure of the governor, which in turn lets air pressure to the top of the diaphragm on the suction valve unloaders, that then extends the rod downward to open and keep open the inlet valves till the pressure in the receiver drops enough for the governor to cut off the feed to the unloaders and the pump starts pumping up again.
eil That is what I first thought but the inlet plate valves are spring loaded open when the pump is stationary. In the photo of the head components I laid them out as they are fitted in the head. Removing the unloader valves you can push the plate valve down to seat it thus blocking the holes in the lower holder. If that is how the situation is until the control pressure is reached when the rod extends to shut the plate valve then what stops the air flowing back out of this inlet port on the piston up stroke with it in the up position? I suppose it must be on the fact that the outlet hole is actually effectively larger than the inlet hole because of the "grill" effect of the lower seating part of that valve. So that difference in area is enough to overcome the outlet valves spring and the air flows into the tank. I was trying to find a way for my system to work as Bill had wrote that the ones he had knowledge of the inlet valve is held open when the rod extends and is in fact spring loaded closed! This confused me and hence the theories! Thanks for your input in clearing it up.
I have purchased a 3hp motor and cast iron pulley but am having second thoughts about using that as a power source. After all it is supposed to be a mobile compressor. At the moment I have my eyes on a Briggs and Stratton 5hp petrol motor. Do you think that will be man enough to power it? I have a new mobile compressor with a Honda engine with what I think is a 3.5hp motor but I think the pump is single cylinder. The problem is working out the pulley size. From what I can gleam from the internet these type of motors(Honda and B&S) seem to rev at full load at 3600rpm. Does that sound right? The motor I have my eye on is an ex army unit with a 5in pulley and a built in clutch. My reckoning means I might have to swap the pulley for a 70mm dia to keep the pumps speed to below the 950rpm.I have a few more checks to make before I commit.
I have purchased a 3hp motor and cast iron pulley but am having second thoughts about using that as a power source. After all it is supposed to be a mobile compressor. At the moment I have my eyes on a Briggs and Stratton 5hp petrol motor. Do you think that will be man enough to power it? I have a new mobile compressor with a Honda engine with what I think is a 3.5hp motor but I think the pump is single cylinder. The problem is working out the pulley size. From what I can gleam from the internet these type of motors(Honda and B&S) seem to rev at full load at 3600rpm. Does that sound right? The motor I have my eye on is an ex army unit with a 5in pulley and a built in clutch. My reckoning means I might have to swap the pulley for a 70mm dia to keep the pumps speed to below the 950rpm.I have a few more checks to make before I commit.
Busy looking at petrol engines to power my compressor. I have come across a make called "Lifan" and they are identical to the Honda GX range. Indeed they are being advertised as such on the ebay. Brand new, an example is for a 6.5hp for £139 delivered. Anybody come across these at all or is it too good to be considered a true bargain?
Fondly enough there is also an item for sale that is a complete/or nearly complete Honda engine in bits and it states that the parts are interchangeable with the "copies". I know some of the makers of engines and indeed other powere tools of this sort do allow other companies to make copies of their makes under a form of licence/agreement. So as you say it is a gamble. Then so is buying a "good" secondhand genuine Honda. At least I suppose you would have at least 12 months guarantee with the "copy". The amount of use I am going to put the compressor to will not by any means hammer it!
Bill Edwards
Member
- Messages
- 4,959
- Location
- Scarborough, North Yorkshire
I've a dim view of cheap copies of decent engines, from generators that haven't lasted long.
Don't expect the seller to actually be around to honor the warranty. If they're still contactable and you manage to get in touch and so on you may find that when you turn up at their business premises they've a nice little trick and they're actually operating out of somewhere else that's next door and you get nowhere when trading standards are called because they didn't replace or refund. I'm had this happen a few years ago, expect to deal with experienced crooks.
With all this said I think there are loads out there that do work and for limited amounts of use the chances are that they'll be just fine, but you certainly need to be aware that the warranty is not to be relied upon, and you already know they won't be built that well. But £139 doesn't seem like that much, I understand your thinking!
Personally I would see what it would cost to get a well respected make, I don't know what you are looking at cost wise, plus there can be the issue of collecting it as delivery isn't likely to be an option like with the new one. But get one and you should always get parts and it'll go for years.
Don't expect the seller to actually be around to honor the warranty. If they're still contactable and you manage to get in touch and so on you may find that when you turn up at their business premises they've a nice little trick and they're actually operating out of somewhere else that's next door and you get nowhere when trading standards are called because they didn't replace or refund. I'm had this happen a few years ago, expect to deal with experienced crooks.
With all this said I think there are loads out there that do work and for limited amounts of use the chances are that they'll be just fine, but you certainly need to be aware that the warranty is not to be relied upon, and you already know they won't be built that well. But £139 doesn't seem like that much, I understand your thinking!
Personally I would see what it would cost to get a well respected make, I don't know what you are looking at cost wise, plus there can be the issue of collecting it as delivery isn't likely to be an option like with the new one. But get one and you should always get parts and it'll go for years.
I am looking at all options at the moment and have my eye on a couple of Biggs and Strattons and a Honda. As we are on about engines I have quite a lot of tools using them some, 2 stroke and some 4 stroke. With a couple of the 4 strokes I have had problems getting them to run after not using them. The first one was one of my lawn mowers. I had used it through the summer as usual for 6 or so years and left it in the shed with fuel in the system, no bother. Then the next cycle I could get it to start and run but it did not like the choke off and revved away. I put up with that for a year but on the next cycle I decided that the dreaded fuel breakdown had occurred and I had to get the carb sonic cleaned. The same thing happened to my Honda powered air compressor. This one went bad after about one year. Again sonic cleaning both the carb and the tank filter cured it. Now I had been introduced to Aspen2 fuel by my friendly tree surgeon to use on my chain saws, as that does not degrade and can last a couple of years. I found that they also do the same for 4 stroke and it is just called Aspen. The 2 stroke product comes in a orange container and the 4 stroke in a blue one. So I decided to get some blue stuff for my 4 stroke machines. The lawn mower, my ride on mower and the compressor. A month or so later, having not used them, I found the stuff had evaporated from the tanks. The 2 stroke product does not though! And it is not cheap! Funnily enough though the sit on mower has never been a problem the eight years I have had it with only minimal use each year and leaving the normal pump fuel in it! Sods law. Anybody else been caught out with this fuel?
eil if the spring keeps the inlet valve shut(assuming that the logic of shut means no flow and open means flow) then what opens it to allow the piston to get the air it needs to compress and deliver to tank? You said the second state is when the rod extends and by virtue of the first state being shut then that state must be open yet in that open state there is no air flow as it is offloaded?
roofman
Purveyor of fine English buckets and mops
- Messages
- 12,165
- Location
- North West with water on 3 sides
Chinese and crankshafts are made of chocolate...find a good used honda,i have 3 for sale
Plus you dont need a 6.5hp on that pumpBill Edwards
Member
- Messages
- 4,959
- Location
- Scarborough, North Yorkshire
I take it then that you never tried emptying the carbs when you weren't likely to be using them for some time?
Some carbs even have a drain on the bottom to do this where you can just push a button and it empties the float chamber.
Otherwise I do it by simply switching off the fuel tap (cheap enough to buy off eBay if not already fitted) and letting it run on what is in there leaving an empty carb. The fuel in the tank may still go off, but it's better than having it go off in the carb too. I guess I'd work on keeping the fuel tank as empty as possible too.
Some carbs even have a drain on the bottom to do this where you can just push a button and it empties the float chamber.
Otherwise I do it by simply switching off the fuel tap (cheap enough to buy off eBay if not already fitted) and letting it run on what is in there leaving an empty carb. The fuel in the tank may still go off, but it's better than having it go off in the carb too. I guess I'd work on keeping the fuel tank as empty as possible too.
I realise that Bill. But some of the machines, like the ride on mower, I use it mainly as a tow machine moving stuff from the house, where the garage is, to the upper main workshop where I have a parking area with the "projects" parked. Again it does not get used a lot, I disconnect the battery after each use, but that takes a minute to reconnect. And as I mentioned, that has never suffered from the problem over the eight years I have had it. Then the brand new compressor with its Honda engine clogged up in months! I reckon some of the aluminium they use in some of the carbs must be more porous than others as that is where the bad fuel soaks into and ruins the flow. When you strip down the carbs you cannot see anything that would be causing the problem and the only thing is a sonic clean.
