Control valve on post rammer

[JoshNZ]

Hello, first time poster here, and first time working on hydraulics so please excuse any ignorance and incorrect terminology etc. I was hoping to get some advice about this control valve on a post rammer Dad has asked me to look at. It had a few issues which I have cleared up just by dissembling and cleaning but there are a couple of remaining things I'm scratching my head about.

1 - I don't think the anvil comes down as quick as it could, is this plummed in the most sensible manner? I have labelled the pictures to give an idea. The spool in use is the one with two passages, the second spool is unused. As far as I understand, it's an open centered spool, when the lever is pulled the cylinder is driven upwards, when released the cylinder is locked and when pushed forward the oil is allowed to dump back into the tank return.

2 - If a hand were to slip off the lever while the anvil was plumetting, is that relief valve setup to cushion that stop, or is this set up to cause damage? I did remove and note that it was a relief valve I just can't quite figure out which pressure it is there to relieve...

I might as well ask, does anyone know what make/model it is? An exploded diagram would really help.

Any advice appreciated of course, and thanks in advance!

 

[oldnslo]

I presume you are asking about the adjustable valve below the tank line in your first picture? If yes does the cavity for this valve connect to the cylinder port? If yes then this would be a work port relief which as you stated would act as a brake or cushion for stopping the ram if the lever is released mid stroke.

Dropping speed is dependent on little or no restriction in the tank line. Is this a self contained system with its own pump and reservoir or does this connect to a tractor or skid loader to supply the hydraulic power?

I have no idea what brand of valve that is.

 

[JoshNZ]

I couldn't see if that valve connected to the working port. I should get a piece of wire and do some proper poking around I suppose.

It is connected to a new Holland tractor at the moment, one of the remotes is put into constant pumping mode and it has a separate low pressure tank return. I realise it's all about the oil escaping quickly, I just wondered if it's likely to be the control valve restricting it or the fittings/hoses etc. For example is the spool in use installed the correct way, for maximum oil flow on release? It's inserted in the handle end, large passage first. I can't see any reason why you can't reverse it it looks like it is designed to be. On a single acting cylinder like this, are both passages on the spool being used? Or are we just using the smaller one. Or have I not understood it right haha.

 

[oldnslo]

Josh,
I am not sure how the valve is made but suspect it is set up to operate a single acting single. Shift the spool one direction and pump flow is directed out to raise the ram. Shift the valve the other direction and I suspect both the pump flow and the ram are connected to tank. If this is true then you could not change how the ram is connected to this valve.

Is there also a quick disconnect on the low pressure return? If yes these create a significant restriction.

Can you install a gauge in the tank line to see what the pressure is while the valve is in neutral Vs when the ram is dropping?

 

[JoshNZ]

Oldnslo, I think you're right about the valve after poking around some more. Reversing spool would only enable the other port to do the same thing. So I'll rule out the valve configuration.

The low pressure return is a threaded fitting. See picture below. The smallest 'choke point' is probably that steel elbow where the ram connects to the valve.

I might have a spare sprayer gauge lying around but nothing designed for hydraulics I don't think. I wondered about propping the anvil up on a post and then disconnecting that ram feed hose, poking it into a bucket then knocking the post out from under the anvil and seeing if it comes down any quicker.



I did check that reliefe valve too, it is obviously relieving the working port pressure so that is good to know. I was told I need a port reliefe valve to prevent cylinder splitting if the handle was fumbled during a drop, but that should take care of that as you said?

 

[oldnslo]

Josh,
Not sure what the flow rate of the pump is on your tractor but can raise the ram then stop the pump flow from the tractor. Then from the ram. This eliminates the tractor pump flow from the return circuit. If you see a speed increase then you know that you have a restriction in the return line. If no change in drop speed then the restriction is from the ram to the outlet port of the valve.

 

[JoshNZ]

Bloody great idea. Standby :thumbsup:

I don't think there is any significant difference, with the pump running or stopped. I edited two videos side by side and the anvil hits a touch earlier with the pump off, but not enough to call it a difference I don't think.

So that means it's either the hose bewteen ram and valve, or the valve itself. Any other ideas to tell which? Dumping the ram into a bucket sounds a bit messy but I guess that would be the final word.

 

[oldnslo]

Josh,
Not sure how you can easily isolate the ram from the valve but possibly try restriction the valve spool travel to see if you notice a speed change when the ram is dropping. Does a small movement make a change? If yes this would indicate the valve is limiting the flow at that point. I suspect it is a combination of the hoses, valve, fittings, etc.

Do you know what size (diameter) the cylinder is? If yes then you can figure the return flow rate based on the cylinder travel speed.

This is the formula I use for cylinder speed Vs flow is:
Q = VA

Q = flow (GPM)
V = cylinder velocity (inches per second)
A = cylinder (square inches)

Example: 2.5 inch diameter cylinder traveling 20 inches per second

2.5 dia = 4.91 sq in area 4.91 times 20 = 98.2 cubic inches second flow time 60 = 5892 cubic inches minute divide 231 = 25.5 GPM

 

[JoshNZ]

Sorry I've had my butt stuck to the tractor the last couple of days.

So the cylinder is 45mm wide. I figured the last half of the anvils fall is close to its terminal velocity so I didn't bother measuring the first half as that would be accelerating. The last half of the fall takes 0.37s and takes 360mm of stroke from the ram, so that's 572786mm3 in .37 seconds, or... .151 US Gallons in .37s which is... 24.5GPM at its fastest, does that sound sensible? Going by my gut I'd say it wants another 6-8gpm to achieve a 'natural' fall.

I couldn't say what the inner diameter of the elbow on that ram is but I measured the OD at 13.7mm, 7/64ths bigger than 1/2" (Geez you guys need to convert!) Is that enough to squish 24.5gpm through?

 

[oldnslo]

Josh,
Your flow rate calculations are very similar to what get converting everything to USA system. On the elbow I figured 1.5 mm wall or 10.7 mm ID at 25 GPM is around 50 PSI pressure drop for an orifice. On an elbow fitting I would expect this number to be 3 or more times greater so 150 PSI (10 Bar) or more. With out knowing the weight of the anvil it it hard to tell but I suspect this could be a problem.

One reference handbook that I have shows an elbow having roughly 6 times the pressure loss as a one foot piece of hose.

Example: if the anvil weighs 450 kg (990 lbs) on the 45 mm bore cylinder would generate 27.6 Bar (400 PSI) 150 PSI in the elbow and another unknown amount through the valve hoses etc could potentially slow the acceleration and drop speed.