Have an IHI Boom pump (19 m height, 1988 year model), and it has some trouble with rising boom specially when it is full expanded and filled with concrete in pipes. Someone told me that it must be a problem with flow control valve, but unfortunately there is no this part for replacement in factory. So want to know if I can adapt another valve from other brand or other pump. If anyone had similar problem before. appreciate any help. Thanks.

Dirty Filters, wrong viscosity hydraulic oil, a bad boom pump on the way out, oversized concrete delivery pipes on the boom, incorrect installation of monoblocks based on oil delivery and pressures, a bad pilot valve (e.g. low resistance to the coil of the pilot valve). One or more of the above are generally the culprits of what you are talking about. Boom should not have physical variable flow control valve, variable speeds should be done through the proportional valve itself.

My old schwing had a weak boom, i replaced the hydraulic pump (they aren't that expensive $1600. ) it rocked after that.. There are equipment pumps and concrete pump the equipment are much smaller and less expensive. On my  Schwing there were two,one ran the boom and one ran the water and agitator.