Pressure Drop Problem

Shabbirali, you should find a check valve in your system right after the pump that prevents back flow in the system. Check the valve for debris or wear that could prevent the valve from properly seating. Sometimes the reasons for not seating are not obvious to the naked eye and you may need too replace the check valve to restore proper operation. These valves can be of the ball or flapper type. One other thing to check is the overpressure valve that protects the system from dangerously high pressures, these to are normally of the ball or flapper design and have an adjuster for setting the correct operating pressures in the system. Please follow up with your results and any additional info that could be helpfull in diagnosing the problem. Another problem could be low nitrogen pressure if you have a nitrogen over hydraulic system. J.Conway

We have accumulator in the system nitrogen gas has been refilled to maintain the pressure,I had replaced the check and the overpressure valve, the oil which was having burned smell has been replaced and the seals which were leaking had been replaced

the hydraulic pump whose vanes were worned out had been replaced

I am doubtful about the performance of the Heat exchanger.I think may be it is undersized if so can anybody help to provide the parameters to design /replaced the heat exchanger

Try this Heat Exchanger manufacturers web sites for sizing calculations:

http://www.youngtouchstone.com/index.htm

Try this Heat Exchanger manufacturers web sites for sizing calculations:

I go through this web sites but coud not find any sizing calculations, is their any other site or source

What is nameplate info on existing heat exchanger?

What is used to cool the heat exchanger? What are temperatures?

What is KW of pump motor?

What is oil flow through heat exchanger?

What is nameplate info on existing heat exchanger?

What is used to cool the heat exchanger? What are temperatures?

What is KW of pump motor?

What is oil flow through heat exchanger?

Water is used to cool the oil, input temperature of water 2 degree centigrade and out put temp of water 8 degree centigrade

oil input temp 30 degree centigrade ,oil output temperature 27 degree centigrade

oil is 10w/30

kw 6

shabbirali, It doesn't look to me that you have a problem with temperature, a high pressure hydraulic system normally creates a lot of heat. One item of great importance is the hydraulic fluid that is used. It is important to use only what the manufacturer has specified or its equivalent. The cleanliness of the oil is so important that the new oil added to the system should be pumped from the container and through exsternal filters specified by the manufacturer before putting in the system. Oil straight from the new container is not always suitable untill refilltered, its that critical for the proper operation of the system. Make sure the filling of the nitrogen is performed exactly as specified by the manufacturer to prevent a hazardous situation. One thing I haven't Seen mentioned yet is the filter, have you changed it yet? Best of luck and be sure to keep us up to date on your progress. J.Conway

we have replaced the filters suction and discharged both, further recommeded oil by the manufacturer is in use

once we have clean the tank completely from inside and then we change the oil

,It is noted if the press is stopped for one hour or more then when the press is started the pressure is good but then after gradually thre pressure goes down and oil is observed hot, then again if we stop the press for one hour or 45 minutes and after resart it is observed that the pressure is good and then same situation is observed that is dropping of pressure after some running

Can you install thermometer next to pressure gage, and run a temp/pressure curve? It seems if temperature rises, press pressure drops. This way, you could see what temperature will cause the press to stop operating. 30°C oil temperature does not seem to be excessive, but the temperature/pressure data would help with determination.

Based on the 6KW pump motor, I would guess you need a heat exhanger to remove 10KW of heat from the oil. Unless you hare dealing with hot clay, environment, or whatever.

You did not give flow rates for oil or water, so I guess these are unknowns. What size piping is connected to heat exchanger? What are approximate dimensions of current heat exchanger?

That web site has changed, However, I looked and there is no info on sizing there. I was going by their catalog which shows how to size a Heat Exchanger from figuring how much heat you are producing to what size Heat Exchanger you need.

There is a list of Heat Exchanger manufacturers at the "Designers Guide" Link here.

http://www.hydraulicspneumatics.com/Directory/Default.aspx

Check it out and see which ones have sizing information or call their 800 Number and talk to an Application Person.

Hi,

If you are trying to select a suitable size charge air cooler then it may be worth contacting Vestas aircoil A/S in Denmark, they manufacture diesel engine charge air coolers. Maybe they can advise.

Hi Shabbirali

Another place to check after you have taken on board all the other comments that are very valid is the cylinder seals. If the cylinder(s) are double acting, the piston seals may be bypassing oil or, perhaps only one of several cylinder seals may be bypassing. This will be creating pressure drop and can be detected (usually by hand) as an increase in heat at the cylinder barrel! This is common on presses that have a high cycle life. It would probably require the seals to be replaced AND the cylinder bore to be re-honed!

If this is the case, for production reasons, it may be prudent to carry a spare cylinder assembly and keep rotating them out on a PM basis!

Good luck with it!

Air in the system will also cause the symptom

Do you have accumulators in the system?

Is it possible that production rate has changed?

If the system at start up is fully pressurised including the accumulator and this then drops with use, the usage of the equipment may be greater than the volumetric capacity of the pump.

Increase in oil volume used could be from "more strokes per minute" or from greater volume used per stroke, either from a replacement cylinder of greater diameter or having made adjustments to require a longer stroke.

All the other suggestions about oil quality and seals are very valid and you seem to have dealt with those. Maybe this can help.

IMO, the problem was caused by not using the press properly. I havent heard about a vane pump being operated at such a very high pressure(260 bars!!!). The maximum pressure that I would use a vane pump is 210(but not maintained/just intermitent). Otherwise you should have used a piston pump or gear pumps that could operate at higher pressures.

In a simple hydraulic press having an accumulator system to help in providing sufficient flow at desired actuator/cylinder speed, you are just trying to maintain the charging of an accumulator. For a semi-automatic system, the components are pump, then a relief valve set slightly higher than the maximum accumulator charge (with venting solenoid) and teed to the pump immediately, then a check valve, then an accumulator(with accessories...like bleed valve and another relief valve), a pressure switch, then a directional control valve(closed P) and any other valves (flow or counterbalance for overruning purpose... if necessary). The pressure switch dictates the loading of the accumulator as well as unloading (venting)of the pump at low(almost zero) pressure. The relief valve should be set slightly higher than the maximum accumulator charging pressure to prevent it from relieving at higher pressure(which cause higher pressure drop[my name] across the relief valve= power loss= heat).

If you are using the press for long hours, then you need heat exchanger(especially if your reservoir is small). You dont need a big one(calculate) if your reservoir oil volume can be 5 times the pump GPM. The relief return line has to be connected to the heat exchanger and I dont mind if you dont connect the T port of the directional valve to the heat exchanger... its fine with me.

BTW make sure that the accumulator should not discharge fully so as not to touch the bladder protection valve very often/not at all during working cycle. Thats why the minimum setting of the pressure switch has to be determined to prevent bladder tear. This would also reflect on the nitrogen pre-charge pressure... For a 18 stroke per minute... I guess an adiabatic calculation is suitable...

" I havent heard about a vane pump being operated at such a very high pressure(260 bars!!!)."

Denison, now part of Parker had/has several size vane pumps that are rated at 4,000 PSI contiuous. They also have some Hybrids that have a Vane Pump with an attached Piston Pump that uses the Piston pump for even higher pressure.