Heald 273A

The traverse action on a machine I am looking at functions at first then will not completely shift the traverse valve to reverse direction. A slight push on the lever will cause it to proceed then will stop again on each reversal. I suspect that the valve is worn and passing by too much oil but would like to hear from someone more familiar with the workings of this valve before I remove the valve. Thanks, Rich

Richard Hammond said:

The traverse action on a machine I am looking at functions at first then will not completely shift the traverse valve to reverse direction. A slight push on the lever will cause it to proceed then will stop again on each reversal. I suspect that the valve is worn and passing by too much oil but would like to hear from someone more familiar with the workings of this valve before I remove the valve. Thanks, Rich

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The convention on hydraulic grinders is that the forward reverse lever controls a pilot spool valve. The pilot valve then directs hydraulic oil to the main forward-reverse spool valve through needle valves which control the dwell time that the table sits at the end of stroke before reversing. The forward-reverse valve requires a minimum volume of oil before it will move fully to the left or right position. The needle valves are used to control the rate at which this oil flows.

If your grinder has been sitting for a while there may be some rust or grit in the pilot valve bore which prevents it from moving to its far left or right position.
The table should be able to exert more than enough force to move the direction lever. The "slight push" needed to make it work suggests that the pressure in your hydraulic system is too low. This could be caused by a stuck pressure relief valve or a worn hydraulic pump. The pump inlet tube sometimes has a strainer installed on it which could also be clogged. Do you know when the hydraulic system was last flushed out?

The spool valves are designed to leak and unless your grinder has been heavily abused will show little or no wear even after 40 years of use. If the pilot valve was badly worn the table would stay stuck in position no mater how hard you pushed the control lever.

In some manifold designs there is a built in leak in the spool valve bores connected to a coil of 1/8 copper tubing. The tubing drains into the hydraulic sump. The leak is there to insure that there is no air trapped in the valve bore. The copper tube will allow air to easily pass through but will only allow a small flow of the viscous oil to drain.

Robert

thanks for your input

Robert R said:

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The convention on hydraulic grinders is that the forward reverse lever controls a pilot spool valve. The pilot valve then directs hydraulic oil to the main forward-reverse spool valve through needle valves which control the dwell time that the table sits at the end of stroke before reversing. The forward-reverse valve requires a minimum volume of oil before it will move fully to the left or right position. The needle valves are used to control the rate at which this oil flows.

If your grinder has been sitting for a while there may be some rust or grit in the pilot valve bore which prevents it from moving to its far left or right position.
The table should be able to exert more than enough force to move the direction lever. The "slight push" needed to make it work suggests that the pressure in your hydraulic system is too low. This could be caused by a stuck pressure relief valve or a worn hydraulic pump. The pump inlet tube sometimes has a strainer installed on it which could also be clogged. Do you know when the hydraulic system was last flushed out?

The spool valves are designed to leak and unless your grinder has been heavily abused will show little or no wear even after 40 years of use. If the pilot valve was badly worn the table would stay stuck in position no mater how hard you pushed the control lever.

In some manifold designs there is a built in leak in the spool valve bores connected to a coil of 1/8 copper tubing. The tubing drains into the hydraulic sump. The leak is there to insure that there is no air trapped in the valve bore. The copper tube will allow air to easily pass through but will only allow a small flow of the viscous oil to drain.

Robert

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Is there a fluid you would recommend for cleaning out the hydraulic system? This machine has set idle for about 10-12 years disassembled.

Richard Hammond said:

Is there a fluid you would recommend for cleaning out the hydraulic system? This machine has set idle for about 10-12 years disassembled.

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The first thing to do is buy a 273A repair and parts manual if you do not already have one. Ebay has several copies for sale at $70.00

Heald 273A, Universal Grinding Machine, Instruct Service & Parts Manual 1969 | eBay

The hydraulic oil in your grinder had, at one time, additives that prevented corrosion. The additives have been consumed after 10 years. The sump needs to be emptied. The tank access plate needs to removed and the sump carefully cleaned out with lint free rags. There will be a large amount of "mud" at the bottom of the tank. The Heald may have a hydraulic oil return line filter. If so, it needs to be replaced. The old rubber sealing ring on the access plate will leak. Apply a bead of RTV sealant to the ring before reinstalling the access plate.

The manual will specify what viscosity oil will be needed. Do not use a NAPA or similar off brand hydraulic oil. The Mobile, Chevron, or Shell products are designed for long service life. You can substitute the equivalent Mobile Vaculine or Chevron products that are intended to be used as both the way oil and the recirculating hydraulic oil. They are slightly more expensive but are much more convenient than stocking two different oils.

The oil should be transferred from the 5 gallon bucket to the sump with a pump running the oil through a filter. The alternative is to slowly pour the oil into the sump and leave the last pint in the bucket. There is often mystery stuff in the bottom of the bucket.

The Heald grinder hydraulics are turned back on with the needle control valves fully open. The spool valves and hydraulic pistons are then run back and forth. If you are lucky every thing works. If not, the grinder hydraulics may have trapped air pockets, the pump pressure may be too low, or one or more spool valves are stuck. The Heald manual will have some suggestions on what to do next. The table piston o-ring seals may have gone flat after sitting for 10 years. Try removing the way covers and check if there is a flood of oil running into the table drains. If the table ways are in bad shape you will need to move over to the "Machine Rebuild Forum" for the expert opinions.

It may be worthwhile to pump the new oil out of the sump after it has run through the system for a while and run it through a filter into a bucket. The oil can then be returned it to the sump. Any grit remaining in the oil will eventually settle out in the sump and form a new "mud layer" at the bottom of the tank.

Robert

Richard Hammond said:

The traverse action on a machine I am looking at functions at first then will not completely shift the traverse valve to reverse direction. A slight push on the lever will cause it to proceed then will stop again on each reversal.

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Make sure the machine is LEVEL and you've burped all the air. They will do that when there's air in the cylinder. It's a low-pressure system, cylinder under the table with leather cups on the piston. Very simple but you have to get the basics right.

That's actually the long travel, not the transverse. And I used to rapid the table back and forth several times in the morning to burp the air, otherwise they are prone to that. Sometimes they will sit for a moment, then go. Annoying. And make sure the draulic fluid level is up or the pump can suck air in, which will then collect in the ends of the table cylinders. It's easy to put new cups on the pistons but the table weighs about a thousand pounds.

Other suggestions ^ are also spot-on, but even when correct Healds have a tendency to do what you describe.

I'm jealous. I love those things.